Hi, Walter,
That's a great idea. Quite often it's almost impossible to know the serials of all the planes participating in a particular battle, so a good solution is using some known planes and add a bunch of generic companions. Plus, skins for all of the He-51 in SCW would make a headache to scroll down the whole list in menu when choosing.
If I may give you my opinion, you need at least a couple of early, grey skins, with different patterns of Saint Andrews crosses, black bars and discs over the wings, and white wing tips . Then a couple or may be 3 different camo later skins. Camos varied a lot as you say. You could do a regular Legion Condor splinter (geometric grey, green, brown) a Spaniard 3 coloured irregular patches scheme and may be a 2 coloured irregular one. Those were the most frequent, I think. For the markings over wings, variation is similar to the early patterns.
They usually had double black disc in every wing, big white St. Andrews crosses, more or less wide white wing tips (sometimes painted so carelessly on top of half a black disc
) and a great variation of black bars or none of them. You can get inspiration from the many great historic skins already made for both periods of SCW.
Thanks in advance.