Whats the differance between R4 red and R6 red colors

Had an LM23P9B, E55, D21, R4, R4, L2X. It's pretty orange. If you parked next to a red car it looked orange. If you put it next to my buddys big block 4spd hugger orange Nova, then it was red. Kind of a reddish/orange, or orangeish/red.