I'm not sure why the sourceforge interface decided to submit my report early, I didn't click anything.
Anyway, the 16 bit (565) to 15 bit (555) color conversion causes a blue tint, because it shifts the lowest bit from green into the highest bit for blue. I'll attach a patch to fix this.
I discovered the problem while looking into http://sourceforge.net/tracker/?func=detail&aid=2999634&group_id=52551&atid=467232 . Part of the problem is that SDL sets up a 15 bit surface that is reported to and/or detected by DOSBox as a 16 bit surface; I was able to fix it by changing the 16 -> 16 bit conversion to the (fixed) 16 -> 15 bit conversion.
Patch to fix the 16 -> 15 bpp color conversion