Building a Doolittle Raider B-25. I have searched all photos I can find. I know the bombers got a fresh paint job just before being loaded on board the Hornet. Question is, did they have the gray belly? I have seen models both with the grey and without.
Going by this link - yes (probably)...
The shot of s/n 40-2281 that didn't make the mission shows a clear colour demarcation - and, to be honest, the shots I've seen of the bombers on the actual mission don't seem to show particularly fresh paint-jobs - there's definite wear and tear visible...
All the best