Thanks folks.
As an example of what I am wanting to do, take a word document with a simple line drawing of perhaps a 3D view of a cube, and I want to be able to apply different colors to the individual sides of the cube. The drawing would most likely be .jpg or similar. On the wish list would also be the ability to do similar work on a .pdf page.
Would the GIMP program do this or would I be better with Photoshop or similar? I have no knowledge of how either of these programs work.
STL