Orks believe that the color red makes things go faster. A basic understanding of the orks reveals that they are all latent psykers and because there are so many of them believing the same thing, they actually warp reality into making these things true. This is why, among other things, their guns work even though they are just metal tubes attached to triggers and handles, why the color red actually does make them go faster, and why things like this actually work.
My question is largely about the Orks, but the Blood Angels offer a good example. Does the color of things used/worn by non-orks matter when in the presence of a large group of orks, if at all? Would fighting orks with red armor on cause you to move faster than if you were wearing white? Would tossing a yellow grenade at them do more damage than a black one?