Cool! Glad you found one. The only SPA 48 machines that I've seen depicted with a blue cowling is the SPAD VII "Black 2", flown by Armand de Turrene that was the main subject of Iain Wylie's cover art for Osprey's Aircraft Of The Aces, Vol 39 -and- the SPAD XIII flown by Roques on Eduard's box art. Osprey's Vol 47 (S.XII & S.XIII Aces) has some photos of them as well and the one flown by Roques appears to have a white cowling. I don't know what inspired Mr. Wylie to put de Turrene's cowling in blue, nor do I know why Aeromaster printed their a/c numbers red.
Of the SPA 48 photos I've seen, all of the cowlings appear to be white. As for the colors of the individual aircraft numbers, on CDL covered SPADs they all look black to me when compared to the unit insignia and rudder markings, whereas on their camouflaged machines they appear to be white.
Please keep in mind that I'm certainly no expert on this stuff; just sharing what I can see in my various references, only a few of which have good photos from SPA 48.