Here's a small addition I have done to Canvas. The code is cleaner than what I send R0j0hound before, so I put here the archive.
If R0j0hound want to integrate it in the main branch, here's what I have done.
The code is pasted at the top of the runtime.js file. I added a "flood fill" action to the edittime.js, with the ID(22). It takes (x,y) and a color name as parameter. The floodfill is nearly instantaneous, but you must use images with clean edges !
You can see in the demo here how to do a "coloring book" app for kids.
(And you can see why you need a clean edges image !)
<img src="http://dl.dropbox.com/u/1412774/CanvasFloodFillDemo/demo.png" border="0">
The .capx :
The demo : http://dl.dropbox.com/u/1412774/CanvasFloodFillDemo/index.html
The plugin : http://dl.dropbox.com/u/1412774/CanvasFloodFillDemo/canvas.modPode.0.1.zip
As always, when I add some code to someone's plugin, I don't claim anything on his realisation, you need to thanks the original author here, R0j0hound !