Choose a color when adding a dataset to the menu

I'm trying to match the legacy color-choosing behavior from before Rapid#1642 (which changed a bunch of things)
This code is a bit weird - I don't like it and we should change it...
- If adding fbRoads/msBuildings, choose "Rapid magenta".
- If adding an Overture dataset, choose "Overture cyan".
- If adding an Esri dataset, choose a color based on how many datasets were added already.

modules/core/RapidSystem.js

@@ -4,6 +4,7 @@ import { Extent } from '@rapid-sdk/math';
 import { AbstractSystem } from './AbstractSystem.js';
 
 const RAPID_MAGENTA = '#da26d3';
+const OVERTURE_CYAN = '#00ffff';
 const RAPID_COLORS = [
   '#ff0000',  // red
   '#ffa500',  // orange
@@ -53,6 +54,7 @@ export class RapidSystem extends AbstractSystem {
     this.acceptIDs = new Set();    // Set<dataID>
     this.ignoreIDs = new Set();    // Set<dataID>
 
+    this._nextColorIndex = 2;  // see note in _datasetsChanged()
     this._taskExtent = null;
     this._isTaskBoundsRect = null;
     this._hadPoweruser = false;   // true if the user had poweruser mode at any point in their editing
@@ -392,7 +394,24 @@ export class RapidSystem extends AbstractSystem {
 
     const enabledIDs = [];
     for (const [datasetID, dataset] of this.catalog) {
-      dataset.added = this._addedDatasetIDs.has(datasetID);
+      // This code is a bit weird - I don't like it and we should change it...
+      // I'm trying to match the legacy color-choosing behavior from before Rapid#1642 (which changed a bunch of things)
+      // - If adding fbRoads/msBuildings, choose "Rapid magenta".
+      // - If adding an Overture dataset, choose "Overture cyan".
+      // - If adding an Esri dataset, choose a color based on how many datasets were added already.
+      const wasAdded = dataset.added;
+      const nowAdded = this._addedDatasetIDs.has(datasetID);
+      if (!wasAdded && nowAdded && dataset.color === RAPID_MAGENTA) {  // being added right now with the default color
+        if (dataset.categories.has('meta') || dataset.categories.has('microsoft')) {
+          dataset.color = RAPID_MAGENTA;
+        } else if (dataset.categories.has('overture')) {
+          dataset.color = OVERTURE_CYAN;
+        } else {
+          dataset.color = RAPID_COLORS[this._nextColorIndex++ % RAPID_COLORS.length];
+        }
+      }
+
+      dataset.added = nowAdded;
       dataset.enabled = this._enabledDatasetIDs.has(datasetID);
 
       if (dataset.added && dataset.enabled) {