There are several, just none that are still maintained. But webkit is still open source and there's no reason someone could not fork or start up a new browser project with 90% of the work already done by webkit, you just need a GUI.
If you are not interested in the edges, only painting the sites with different colors, you can use a variation of flood fill starting with the seeds and only stacking the pixel if that color has distance lower than the one already painted that pixel.