On the issue of cost... I think it's a pretty safe bet that, in general, a mostly solid colored figure who is cast in his primary color costs less... Paint aps are generally a lesser cost though in the grand scheme too... Depends on the # of colors, the complexity, etc...
Like, for instances, there's camo paintjobs on some figures I buy... Some are complex, others aren't so much, but the complex ones probably cost more. Decals are another thing to think of too, like for instance the emblems on an X-Wing pilot's helmet which aren't necessarilly a paint application so much as a decal that's set into the figure.
I think paint's pretty negligible as far as it being an individual cost goes though. Production overall is a lot of little costs though, which are what add up... With a few big ones. The big ones usually stay fixed though, and wind up being littler costs when spread over a whole products run.
Like, for the 1:18 military line(s) I collect, they have a real fine balance as far as what planes to make. They have to figure how many units will SURELY sell and things... There's a huge debate raging right now because they're dumping the Jap. Zero, which fans want but the company says all the new toolings would be tough to justify what they feel what be limited sales... Especially because they rely heavily on repainting the vehicles, which works AOK most of the time, but with the Zero it wouldn't since there really weren't a ton of paint variations of it. It kinda came one color and that was that.
Anyway, that's that... I'd say Stormies are pretty simple paintjobs (little detail work on those helmets though), but in the end paint aps aren't the costliest production factor in and of themselves anyway.
And on the red battledroid issue...
I dunno. I thought EU was claiming they had a few different sort of generic colors for sort of generic placement of them. Green for one terrain, tan for another, red for another... I'm not sure about that of course, I just recall seeing those 3 colors in one of those Holo-Net News reports in Insider once.
I know in the production scenes of Battledroids in AOTC, you can see them being sprayed with something that's covering them... What it is, I dunno. They do match the coloring of geonosis though so it seems like it could easily be some vague attempt at making them tougher to spot.
That's been my thought on the paintjobs, but I don't know that anything has taken any great length to give it an official LFL explanation either... Anyone?