People who take stellar photos of their art:

How you do???

Seriously, I try to take pictures of my art that has a white background and it doesn’t matter if it’s in direct sunlight, overcast light, indoor light, etc., the white is ALWAYS gray.  And I try to edit that out on GIMP or whatever and it never works.  It just makes the colors garish and I lose all my midtones.

Any advice or spells I could use?