Well, the helmet, maybe, which is probably another trademarked design. The uniform itself, if you removed all the fonts and lettering and presented a logoless jersey... maybe. The color helps to make it unique, but it's not the whole thing. If you were talking about medical professionals, though, I can see where the idea of the color being integral to the identification holds up. So yeah, there are reasons to trademark particular colors, I guess. I just never really thought that a concept like "this wavelength of the visible light spectrum" was a trademarkable thing.