initial draft

src/bg.js

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+var getFavicon = function(){
+	var favicon = undefined;
+	var nodeList = document.getElementsByTagName("link");
+	for (var i = 0; i < nodeList.length; i++)
+	{
+		if ((nodeList[i].getAttribute("rel") == "icon") || (nodeList[i].getAttribute("rel") == "shortcut icon")) {
+			favicon = nodeList[i].getAttribute("href");
+		}
+	}
+	return favicon;
+}
+
+var changeIcon = function(color) {
+	var canvas = document.createElement('canvas');
+	canvas.width = 16;
+	canvas.height = 16;
+	var ctx = canvas.getContext('2d');
+	var img = new Image();
+	img.src = getFavicon();
+	img.onload = function() {
+		ctx.drawImage(img, 0, 0);
+		ctx.fillStyle = color;
+		ctx.fillRect(0, 0, 2, 16);
+
+		var link = document.createElement('link');
+		link.type = 'image/x-icon';
+		link.rel = 'shortcut icon';
+		link.href = canvas.toDataURL("image/x-icon");
+		document.getElementsByTagName('head')[0].appendChild(link);
+	}
+}
+
+var generateRandomColor = function(seed) {
+	var selectColor = function (colorNum, colors){
+		if (colors < 1) {
+			colors = 1; // defaults to one color - avoid divide by zero
+		}
+		return "hsl(" + (colorNum * (360 / colors) % 360) + ",100%,50%)";
+	}
+
+	return selectColor(seed, 8);
+}
+
+changeIcon(generateRandomColor(1));

src/manifest.json

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+{
+  "description": "color tabs based on their parent.",
+  "manifest_version": 2,
+  "name": "colortabgroups",
+  "version": "0.0.1",
+  "homepage_url": "https://git.e.tern.al/s2/colortabgroups",
+}