Add color provider hook to manage what colors are assigned to which node

packages/ott-vis-panel/src/colors.ts

@@ -1,12 +1,23 @@
+import * as d3 from "d3";
+
 class ColorProvider {
+	private color: d3.ScaleOrdinal<string, string>;
+	private assignments: Map<string, string>;
+
+	constructor() {
+		this.color = d3.scaleOrdinal(d3.schemeCategory10);
+		this.assignments = new Map();
+	}
+
 	public assign(thing: string): string {
-		// TODO: implement
-		return "";
+		if (!this.assignments.has(thing)) {
+			this.assignments.set(thing, this.color(thing));
+		}
+		return this.assignments.get(thing) as string;
 	}
 
-	public assignments(): Map<string, string> {
-		// TODO: implement
-		return new Map();
+	public getAssignments(): Map<string, string> {
+		return this.assignments;
 	}
 }