Texturing in blender for Aeson model

So, a while back, I went and got the model for the Aeson commander and put it into blender. (with much help of course!!!) Now, I am doing the same with Osiris. I am hoping to make lego models of both, Aeson for me and Osiris for my friend, I am texturing Aeson right now so I get an idea of color, but, is there a way to separate the pieces of the Uv wrap so that when I use the fill option when painting, it does not paint the hole Uv sheet that color, like make it so that it only fills that small piece?

Thanks!! Once again, I am a blender noob right now!!

Your best option is to export the uv as png and colour it in gimp or Photoshop then apply it again.