add ability to provide custom preview colorizer

src/mode/fdm/prepare.js

@@ -413,10 +413,16 @@
         let lastOut = null;
         let current = null;
 
-        function color(point) {
+        function colorDefault(point) {
             return hsv2rgb({h:point.speed / maxspd, s:1, v:0.75}, true);
         }
 
+        function colorCustom(point) {
+            return FDM.rateToColor(point.speed, maxspd);
+        }
+
+        const color = FDM.rateToColor ? colorCustom : colorDefault;
+
         levels.forEach((level, index) => {
             const prints = {};
             const moves = [];