If I want spot colour I usually place those at the base, for soldiers in green jungle uniform that may for an example be a red or orange flower.

Gotta agree with Malebolgia here. Colour theory always works, period. But colour theory doesn't tell you what colour to use to paint something, just which colours compliment each other or contrast with each other for maximum visual effect. For miniature painting, contrast is something you want if you desire your miniatures to stand out and that's where personal choice comes into it.

If your favour realism above all else then you can still create something that looks good up close, or cohesive when arranged for a group shot. But at a distance of three feet or so, those minis are going to be indistinguishable from each other, and perhaps the terrain too since we don't usually have the luxury of spot lights for our minis once they are on the tabletop.

But honestly when it comes to a Brotherhood scheme my first thought is to unify them with their bases and paint them as they are in the artwork. In my mind, the Brotherhood never wore camouflage no matter where they were deployed because they were supposed to be visible and indeed, recognisable by their armour style and colouration. So, black highlighted with dark blue for the Mortificators, red and black highlighted with blue for the Inquisition and so on.

If you wanted a more consistent colour scheme though, it's hard to ignore the white and gold look just as long as you can pull off the bright, clean white that you need.

The colour wheel is an invention, a cultural construct, real colours are wavelengths of light and not cyclical after red comes infra-red not purple and after purple comes ultraviolet not red. There's no reason that green and red should be opposites, they are not, two colours opposite would be black (or a shade of grey actually, absorb light equally on all wavelengths) together not brown or green.

I have no problem with contrasts, they can be a useful tool but they arent a rule to be slave to, like I said earlier there have been other colour theories down the ages, the chivalric system of metallic and non metallic for an example.

The current (for a few hundred years or so) color theory that is discussed looks and works fine in my opinion and that's good enough for me. I seldom use direct opposites but I think it looks better with more contrast in the color schemes than using only realistic colours. Just a hint of something blue or green among red does wonders in lifting a small mini

For my Brotherhood, I'll obviously going for the traditional red/black for the Inqs and Blue/black for the mortificators. For the troopers and possibly Judicator I'll probably go for mainly metal/silver with red,blue or purple details - I want a knighly feel about them. I just hope the minis arrive soon...