I did something funny like that a few years back trying to apply textures to roads for a game on top of the map. I normalized all the road colors to make it eas

I did something funny like that a few years back trying to apply textures to roads for a game on top of the map. I normalized all the road colors to make it easy to pick out, then drew the texture on them with canvas (my memory is a little hazy here). It worked well, surprisingly.