Of course, but I do think we should consider both effects.
Perhaps some of you could experiment with Blood-Angels with Ultramarine allies, divide your deployment in two and see which side your opponent considers most threatening?
That's a poor idea because Blood Angels and Ultras are, though similar are mechanically different. A blood angel land raider IS more threatening then an ultramarine one because it is faster.
A better test would be two identical codex's with identical army lists, but one with red models the other with blue, and then track the loss and win rate of the two against each other with each list playing a wide verity of different codex's and army lists and tracking who gets first blood, who gets more victory points on average and the survival rate of different units, (does the red land raider die more often then then blue one)