Here's some images that may help you out, or confuse you!
Interpreting color images from this period can sometimes be difficult as there are many factors to consider. Just too many variables to get into unless you want me to write a small book.
Although I will say that the selection below illustrates very well the difficulties involved!
Nevertheless, color photos of the time are still among our best clues as to what stuff looked like back then.
Sorry for the scan-lines, I gotta get a new machine...
Older & R.T.
3rd Sqn, Kunming, May '42 - This is one shot that seems to support the idea that at least some of the AVG Hawks may have had blue undersides. This photo is scrutinized closely in Tommy Tullis'
Tigers Over China, which I recommend as one of many excellent references on this subject.
3rd Sqn, Photoflight 3, Older #68
Tommy Haywood's #49
R.T. & #40
R.T. & #40 Closeup
I've got several more color shots, some which are useful and some which are just plain cool to look at, which I can scan if you like. Also, I've got a ton of b/w stuff; so if you decide on a particular aircraft, chances are I've got an image of it.
Fade to Black...