Chris - you're probably right.. usually the Marine AC were wearing the same color as the Navy... the SBD-2 I did from VMSB-241was light blue/grey with light grey undersides... it would be a fair bet the Buffalo would look the same...
here's an artists rendition of one of the Buffalos from Midway... note the AC number in black paint... if your decals are white I wouldn't be put out by that... it's hard to find scale numbers for a smaller craft and in the right font...
http://hsgalleries.com/buffalobb_1.htm
I noticed a navy.mil pic of a Marine VMF-221 Martlet Wildcat on Midway after the battle and it had the black markings as well...
http://www.history.navy.mil/photos/images/g10000/g11636c.htm