diff --git a/js/CellSet.js b/js/CellSet.js
index 7b74eed..e7d7439 100644
--- a/js/CellSet.js
+++ b/js/CellSet.js
@@ -1,35 +1,59 @@
 function CellSet(definition) {
 	definition = definition || {};
 	this.cells = {};
-	if(definition.shape == 'rectangle') {
-		var xMax = definition.x + definition.width;
-		var yMax = definition.y + definition.height;
-		for(var i = definition.x; i < xMax; i++) {
-			for(var j = definition.y; j < yMax; j++) {
-				this.add(i, j);
-			}
-		}
-	} else if(definition.shape == 'points') {
-		for(var i = 0; i < definition.points.length; i++) {
-			this.cells[id(definition.points[i].i, definition.points[i].j)];
-		}
+	if(definition.type == 'rectangle') {
+		this.fromRectangle(definition);
+	} else if(definition.type == 'isochrome') {
+		this.fromIsochrome(definition);
 	}
 }
 
+CellSet.prototype.fromRectangle = function(definition) {
+	var xMax = definition.x + definition.width;
+	var yMax = definition.y + definition.height;
+	for(var i = definition.x; i < xMax; i++) {
+		for(var j = definition.y; j < yMax; j++) {
+			this.add(i, j);
+		}
+	}
+};
+
+CellSet.prototype.fromIsochrome = function(definition) {
+	var originColor = definition.data[definition.x][definition.y];
+	var queue = [{i: definition.x, j: definition.y}];
+	while(queue.length > 0) {
+		var p = queue[0];
+		this.add(p.i, p.j);
+		for(var d = -1; d < 2; d += 2) {
+			[{i: p.i + d, j: p.j}, {i: p.i, j: p.j + d}].forEach(
+				gateKeeper(this, definition.data, queue, originColor)
+			);
+		}
+		queue.shift();
+	}
+};
+
 CellSet.prototype.add = function(i, j) {
 	this.cells[id(i, j)] = true;
-}
+};
 
 CellSet.prototype.remove = function(i, j) {
 	delete this.cells[id(i, j)];
-}
+};
 
 CellSet.prototype.contains = function(i, j) {
 	return !!this.cells[id(i, j)];
-}
+};
 
 CellSet.prototype.isEmpty = function() {
 	return Object.keys(this.cells).length < 1;
+};
+
+CellSet.prototype.iter = function(f) {
+	for(var key in this.cells) {
+		var coordinates = key.split(':');
+		f(coordinates[0], coordinates[1]);
+	}
 }
 
 return {
@@ -39,3 +63,13 @@ return {
 function id(i, j) {
 	return i + ':' + j;
 }
+
+function gateKeeper(cellSet, data, queue, originColor) {
+	return function(p1) {
+		if(p1.i >= 0 && p1.i < data.length && p1.j >= 0 && p1.j < data.length
+			&& !cellSet.contains(p1.i, p1.j)
+			&& data[p1.i][p1.j] == originColor) {
+			queue.push(p1);
+		}
+	}
+}
diff --git a/js/Grid.js b/js/Grid.js
index e6ed61b..29599af 100644
--- a/js/Grid.js
+++ b/js/Grid.js
@@ -39,7 +39,7 @@ function makeRow(config) {
 function clear() {
 	grid.data = generate(function() {return; });
 	grid.missing = CellSet.make(
-		{shape: 'rectangle', x: 0, y: 0, width: 8, height: 8}
+		{type: 'rectangle', x: 0, y: 0, width: 8, height: 8}
 	);
 	iter(function(row, column) {
 		cell(row, column).className = '';
diff --git a/js/Grid/Color.js b/js/Grid/Color.js
index cefdba9..041c557 100644
--- a/js/Grid/Color.js
+++ b/js/Grid/Color.js
@@ -15,28 +15,8 @@ function colorize(row, column, color) {
 }
 
 function paint(i0, j0) {
-	var originColor = Grid.get().data[i0][j0];
-	var done = CellSet.make();
-	var queue = [{i: i0, j: j0}];
-	while(queue.length > 0) {
-		var p0 = queue[0];
-		colorize(p0.i, p0.j);
-		done.add(p0.i, p0.j);
-		extend(p0, queue, done, originColor);
-		queue.shift();
-	}
+	var cellSet = CellSet.make(
+		{type: 'isochrome', x: i0, y: j0, data: Grid.get().data}
+	);
+	cellSet.iter(colorize);
 }
-
-function extend(p0, queue, done, originColor) {
-	var size = Grid.get().size;
-	for(var d = -1; d < 2; d += 2) {
-		[{i: p0.i + d, j: p0.j}, {i: p0.i, j: p0.j + d}].forEach(function(p1) {
-			if(p1.i >= 0 && p1.i < size && p1.j >= 0 && p1.j < size
-				&& !done.contains(p1.i, p1.j)
-				&& Grid.get().data[p1.i][p1.j] == originColor) {
-				queue.push(p1);
-			}
-		});
-	}
-}
-