Always good to get a fresh set of eyes on things … The decal/kit instructions I’ve seen for ML-KNIL B-339s give the underside color as aluminum. Also seems to be the official spec. However, photos of ones in the DEI look (to my eye) to be light grey. First photo is (I suspect) demo/ pre delivery at the Brewster factory field. (there are a number of photos with NX3180). It has an aluminum prop and it looks a different shade than the underside. Second is another aircraft (NX3418) at the Brewster facility, again with aluminum prop for reference… Last 3 are B-396 being assembled in DEI. Undersides just dont look aluminum to me. (only reference is the open radio compartment hatch (aluminum?) / underside “paint”.) Brewster used Dupont (I use their lures when fishing.) RAF equivalents on the RAF ones. Dupont “Sky” on the Duch batch? Anybody confirm or deny? Also, deck aft of the pilot seat… aluminum? Only photo I found of any help is one of a Belgian contract one and it looks aluminum. Brewster Buffalo in Dutch Service - Destination’s Journey (destinationsjourney.com)
