Here’s a webpage that claims to have color photos from WWI. It looks reasonably legit from what I can see, but I can’t say for sure.
Click on over and have a look.
UPDATE
Reader Paul Stinchfield has sent me two links where WWI color photos may be found. They are this one and this one.
If you’re interested in looking over a huge online archive of French photographic pioneers, then I suggest that you click this link and start browsing. Lots of stuff there.
(Hat tip to Spoons, and he got from Vodkapundit.)