Red is not as bad as SOME colors (looking at you, blue and yellow) but it's not the right color and thus offends him on principle.

Like Vincent, for example. Vincent offends him on principle, wearing crimson like a goddamn flag. The glare the ex-Turk is given as Heat stalks back to his vehicle with his newest bit of salvaged orange, could wither a cactus.

It's like Vincent breathing the same AIR he is, is somehow deeply obnoxious. "Move." It's not that the gunman is in his way. It's that Heat's going to alter his trajectory to force him to anyway. Goddamn uppity Maribel.