diff --git a/src/components/App.tsx b/src/components/App.tsx
index 89cdf72..3f98f4c 100644
--- a/src/components/App.tsx
+++ b/src/components/App.tsx
@@ -26,6 +26,9 @@ export function App({initialState, statePersister, fs}: {initialState: State, st
       } else if (event.key === 'F6') {
         event.preventDefault();
         model.render({isPreview: false, now: true})
+      } else if (event.key === 'F7') {
+        event.preventDefault();
+        model.export();
       }
     };
     window.addEventListener('keydown', handleKeyDown);
diff --git a/src/components/ExportButton.tsx b/src/components/ExportButton.tsx
index 0a39cd5..4e27ad4 100644
--- a/src/components/ExportButton.tsx
+++ b/src/components/ExportButton.tsx
@@ -1,10 +1,10 @@
-import React, { useContext } from 'react';
+import React, { useContext, useState } from 'react';
 import { ModelContext } from './contexts';
 
 import { SplitButton } from 'primereact/splitbutton';
 import { MenuItem } from 'primereact/menuitem';
 
-type ExtendedMenuItem = MenuItem & { buttonLabel: string };
+type ExtendedMenuItem = MenuItem & { buttonLabel?: string };
 
 export default function ExportButton({className, style}: {className?: string, style?: React.CSSProperties}) {
     const model = useContext(ModelContext);
@@ -56,6 +56,14 @@ export default function ExportButton({className, style}: {className?: string, st
           icon: 'pi pi-file',
           command: () => model!.setFormats(undefined, '3mf'),
         },
+        {
+          separator: true
+        },
+        {
+          label: 'Edit materials' + ((state.params.extruderColors ?? []).length > 0 ? ` (${(state.params.extruderColors ?? []).length})` : ''),
+          icon: 'pi pi-cog',
+          command: () => model!.mutate(s => s.view.extruderPickerVisibility = 'editing'),
+        }
       ];
 
     const exportFormat = state.is2D ? state.params.exportFormat2D : state.params.exportFormat3D;
diff --git a/src/components/Footer.tsx b/src/components/Footer.tsx
index b6c022f..a604f25 100644
--- a/src/components/Footer.tsx
+++ b/src/components/Footer.tsx
@@ -10,6 +10,7 @@ import { Toast } from 'primereact/toast';
 import HelpMenu from './HelpMenu';
 import ExportButton from './ExportButton';
 import SettingsMenu from './SettingsMenu';
+import MultimaterialColorsDialog from './MultimaterialColorsDialog';
 
 
 export default function Footer({style}: {style?: CSSProperties}) {
@@ -19,7 +20,6 @@ export default function Footer({style}: {style?: CSSProperties}) {
   
   const toast = useRef<Toast>(null);
 
-  
   const severityByMarkerSeverity = new Map<monaco.MarkerSeverity, 'danger' | 'warning' | 'info'>([
     [monaco.MarkerSeverity.Error, 'danger'],
     [monaco.MarkerSeverity.Warning, 'warning'],
@@ -72,7 +72,7 @@ export default function Footer({style}: {style?: CSSProperties}) {
               />
         ) : undefined
       }
-      {/* <RenderExportButton /> */}
+      <MultimaterialColorsDialog />
       {/* <Button
         icon="pi pi-bolt"
         onClick={() => model.render({isPreview: false, now: true})}
diff --git a/src/components/MultimaterialColorsDialog.tsx b/src/components/MultimaterialColorsDialog.tsx
new file mode 100644
index 0000000..c995aa4
--- /dev/null
+++ b/src/components/MultimaterialColorsDialog.tsx
@@ -0,0 +1,119 @@
+import chroma from 'chroma-js';
+import React, { useContext, useState } from 'react';
+import { ColorPicker } from 'primereact/colorpicker';
+import { Button } from 'primereact/button';
+import { InputText } from 'primereact/inputtext';
+import { ModelContext } from './contexts';
+import { Dialog } from 'primereact/dialog';
+
+export default function MultimaterialColorsDialog() {
+    const model = useContext(ModelContext);
+    if (!model) throw new Error('No model');
+    const state = model.state;
+
+    const [tempExtruderColors, setTempExtruderColors] = useState<string[]>(state.params.extruderColors ?? []);
+
+    function setColor(index: number, color: string) {
+        setTempExtruderColors(tempExtruderColors.map((c, i) => i === index ? color : c));
+    }
+    function removeColor(index: number) {
+        setTempExtruderColors(tempExtruderColors.filter((c, i) => i !== index));
+    }
+    function addColor() {
+        setTempExtruderColors([...tempExtruderColors, '']);
+    }
+
+    const cancelExtruderPicker = () => {
+        setTempExtruderColors(state.params.extruderColors ?? []);
+        model!.mutate(s => s.view.extruderPickerVisibility = undefined);
+    };
+    const canAddColor = !tempExtruderColors.some(c => c.trim() === '');
+    
+    return (
+        <Dialog 
+            header="Multimaterial Color Picker" 
+            visible={!!state.view.extruderPickerVisibility} 
+            onHide={cancelExtruderPicker}
+            footer={
+                <div>
+                    <Button label="Cancel" icon="pi pi-times" onClick={cancelExtruderPicker} className="p-button-text" />
+                    <Button 
+                    label={state.view.extruderPickerVisibility == 'exporting' ? "Export" : "Save"}
+                    icon="pi pi-check"
+                    disabled={!tempExtruderColors.every(c => chroma.valid(c))}
+                    autoFocus
+                    onClick={e => {
+                        model!.mutate(s => {
+                            s.params.extruderColors = tempExtruderColors;
+                            s.view.extruderPickerVisibility = undefined;
+                        });
+                        if (state.view.extruderPickerVisibility === 'exporting') {
+                            model!.export();
+                        }
+                    }} />
+                </div>
+            }
+        >
+            <div className="flex flex-column align-items-center">
+                <div>
+                To print on a multimaterial printer using PrusaSlicer, BambuSlicer or OrcaSlicer, we map the model's colors to the closest match in the list of extruder colors.
+                </div>
+                <div>
+                Please define the colors of your extruders below.
+                </div>
+                
+                <div className="p-4">
+
+                    <div className="flex flex-wrap gap-2" style={{
+                        flexDirection: 'column',
+                    }}>
+                        {tempExtruderColors.map((color, index) => (
+                            <div key={index} className="flex items-center gap-2">
+                                <ColorPicker
+                                    value={chroma.valid(color) ? chroma(color).hex() : 'black'}
+                                    onChange={(e) => e.value && setColor(index, chroma(e.value.toString()).name())}
+                                />
+                                <InputText
+                                    value={color}
+                                    autoFocus={color === ''}
+                                    invalid={color.trim() === '' || !chroma.valid(color)}
+                                    onKeyDown={(e) => {
+                                        if (e.key === 'Enter' && canAddColor) {
+                                            e.preventDefault();
+                                            addColor();
+                                        }
+                                    }}
+                                    onChange={(e) => {
+                                        let color = e.target.value;
+                                        try {
+                                            color = chroma(e.target.value).name();
+                                            console.log(`color: ${e.target.value} -> ${color}`);
+                                        } catch (e) {
+                                            // ignore
+                                            console.error(e);
+                                        }
+                                        setColor(index, color);
+                                    }}
+                                />
+                                <Button
+                                    icon="pi pi-times"
+                                    text
+                                    onClick={() => removeColor(index)}
+                                    className="p-button-danger p-button-sm"
+                                />
+                            </div>
+                        ))}
+                        <div>
+                            <Button
+                                label="Add Color" 
+                                disabled={!canAddColor}
+                                icon="pi pi-plus"
+                                text
+                                onClick={addColor} className="p-button-sm" />
+                        </div>
+                    </div>
+                </div>
+            </div>
+        </Dialog>
+    );
+}
\ No newline at end of file
diff --git a/src/io/export_3mf.ts b/src/io/export_3mf.ts
index e3e630d..5fb15ab 100644
--- a/src/io/export_3mf.ts
+++ b/src/io/export_3mf.ts
@@ -28,11 +28,28 @@ function getColorMapping(colors: chroma.Color[], projectedColors: chroma.Color[]
 // Reverse-engineered from PrusaSlicer / BambuStudio's output.
 const PAINT_COLOR_MAP = ['', '8', '0C', '1C', '2C', '3C', '4C', '5C', '6C', '7C', '8C', '9C', 'AC', 'BC', 'CC', 'DC'];
 
-export function exportOffTo3MF(data: IndexedPolyhedron, extruderColors?: chroma.Color[]): Blob {
+export function export3MF(data: IndexedPolyhedron, extruderColors?: chroma.Color[]): Blob {
     const objectUuid = uuidv4();
     const buildUuid = uuidv4();
-    const paintColorByColorIndex = extruderColors &&
-        getColorMapping(data.colors.map(c => chroma.rgb(...c)), extruderColors).map(i => PAINT_COLOR_MAP[i]);
+
+    const dataColors = data.colors.map(([r, g, b, a]) => chroma.rgb(r*255, g*255, b*255, a*255));
+    const extruderIndexByColorIndex = extruderColors &&
+        getColorMapping(dataColors, extruderColors);
+
+    if (extruderColors) {
+        console.log('Extruder colors:');
+        for (const c of extruderColors) {
+            console.log(`- ${c.name()}`);
+        }
+        console.log('Model color mapping:');
+        dataColors.forEach((from, i) => {
+            const extruderIndex = extruderIndexByColorIndex![i];
+            const to = extruderColors[extruderIndex];
+            console.log(`- ${from.name()} -> ${to?.name()} (${PAINT_COLOR_MAP[extruderIndex]})`);
+        });
+    }
+
+    const paintColorByColorIndex = extruderIndexByColorIndex?.map(i => PAINT_COLOR_MAP[i]);
     
     const archive = {
         '3D/3dmodel.model': new TextEncoder().encode([
diff --git a/src/io/import_off.ts b/src/io/import_off.ts
index 7c4e412..53400e7 100644
--- a/src/io/import_off.ts
+++ b/src/io/import_off.ts
@@ -47,7 +47,8 @@ export function parseOff(content: string): IndexedPolyhedron {
         let colorIndex = colorMap.get(colorKey);
         if (colorIndex == null) {
             colorIndex = colors.length;
-            colors.push(color);
+            const [r, g, b, a] = color;
+            colors.push([r, g, b, a ?? 1]);
             colorMap.set(colorKey, colorIndex);
         }
 
diff --git a/src/state/app-state.ts b/src/state/app-state.ts
index e7ac7d9..3d4f8c7 100644
--- a/src/state/app-state.ts
+++ b/src/state/app-state.ts
@@ -32,11 +32,12 @@ export interface State {
     features: string[],
     exportFormat2D: keyof typeof VALID_EXPORT_FORMATS_2D,
     exportFormat3D: keyof typeof VALID_EXPORT_FORMATS_3D,
+    extruderColors?: string[],
   },
 
   view: {
     logs?: boolean,
-    extruderPicker?: boolean,
+    extruderPickerVisibility?: 'editing' | 'exporting',
     layout: {
       mode: 'single',
       focus: SingleLayoutComponentId,
diff --git a/src/state/fragment-state.ts b/src/state/fragment-state.ts
index e6841ed..c1c8aa6 100644
--- a/src/state/fragment-state.ts
+++ b/src/state/fragment-state.ts
@@ -66,12 +66,13 @@ export async function readStateFromFragment(): Promise<State | null> {
           vars: params?.vars, // TODO: validate!
           // Source deserialization also handles legacy links (source + sourcePath)
           sources: params?.sources ?? (params?.source ? [{path: params?.sourcePath, content: params?.source}] : undefined), // TODO: validate!
-          exportFormat2D: validateStringEnum(params?.exportFormat, Object.keys(VALID_EXPORT_FORMATS_2D), s => 'svg'),
-          exportFormat3D: validateStringEnum(params?.exportFormat, Object.keys(VALID_EXPORT_FORMATS_3D), s => 'glb'),
+          exportFormat2D: validateStringEnum(params?.exportFormat2D, Object.keys(VALID_EXPORT_FORMATS_2D), s => 'svg'),
+          exportFormat3D: validateStringEnum(params?.exportFormat3D, Object.keys(VALID_EXPORT_FORMATS_3D), s => 'glb'),
+          extruderColors: validateArray(params?.extruderColors, validateString, () => undefined as any as []),
         },
         view: {
           logs: validateBoolean(view?.logs),
-          extruderPicker: validateBoolean(view?.extruderPicker),
+          extruderPickerVisibility: validateStringEnum(view?.extruderPickerVisibility, ['editing', 'exporting'], s => undefined),
           layout: {
             mode: validateStringEnum(view?.layout?.mode, ['multi', 'single']),
             focus: validateStringEnum(view?.layout?.focus, ['editor', 'viewer', 'customizer'], s => false),
diff --git a/src/state/model.ts b/src/state/model.ts
index 3fd996a..7ea8ce5 100644
--- a/src/state/model.ts
+++ b/src/state/model.ts
@@ -11,7 +11,8 @@ import { ProcessStreams } from "../runner/openscad-runner";
 import { is2DFormatExtension } from "./formats";
 import { parseOff } from "../io/import_off";
 import { exportGlb } from "../io/export_glb";
-import { exportOffTo3MF as export3MF } from "../io/export_3mf";
+import { export3MF } from "../io/export_3mf";
+import chroma from "chroma-js";
 
 export class Model {
   constructor(private fs: FS, public state: State, private setStateCallback?: (state: State) => void, 
@@ -208,6 +209,10 @@ export class Model {
         return;
       }
     }
+    if (!this.state.is2D && this.state.params.exportFormat3D == '3mf' && !this.state.params.extruderColors) {
+      this.mutate(s => this.state.view.extruderPickerVisibility = 'exporting');
+      return;
+    }
     this.mutate(s => {
       s.currentRunLogs ??= [];
       s.exporting = true;
@@ -225,7 +230,7 @@ export class Model {
       if (exportFormat === '3mf') {
         const start = performance.now();
         const data = parseOff(await this.state.output.outFile.text());
-        const exportedData = export3MF(data);
+        const exportedData = export3MF(data, this.state.params.extruderColors?.map(c => chroma(c)));
         const elapsedMillis = performance.now() - start;
         output = {
           outFile: new File([exportedData], this.state.output.outFile.name.replace('.off', '.3mf')),