Base coats

Doogs Models has the best video tutorial on this technique.  It works well on gray aircraft models.  It can work on armor. The final color coat is usually thinned well beyond 50%.

Base coat black...mottle coat of finish color allowed to fully dry....then very thin final coat

Like anything it takes practice to get right.

Its called black baseing, several members here use it. I have only seen it done with black, hence the name. I guess red would possable work, i think the main thing is the background colour needs to be darker. But the paint you then apply should be in thin coats and i would imagine the red would effect the final colour.