Are the greyscale cameos automatically generated from the existing ones, or is it possible to have a different effect when a unit / upgrade cannot be built? There doesn't seem to be any references to the greyscale images, implying they are automatically created.
This is a pain, because as a WWI mod all our cameos are b/w :\
Do your cameos have to be pure greyscale? You could always add just a slight tinge of a colour to it, that way you would know if it was available or not but it wouldn't be as bad as making them full color.
AFAIK, yes. IIRC, in the beta it was not, and the cameos were created by EA for the different states. I guess one could check that code, and see if it still works.