whenever you render an picture, it comes out as a picture file (jpeg, png, etc.)

just open the picture from the photo-editor.

for modifying the body part colors, you just need to go to the Surfaces tab. it should be somewhere in the Tools section of DAZ. from there, go to advanced and play around.

if you want to do a more direct modification, go to the DAZ runtime files, find the Textures file, and open up whatever you want to modify. (C: > Program Files > DAZ > Studio > Content > Runtime > Textures > etc...)