What is the inyan of not wearing red clothing? Does it matter how much of the clothing has red? (a small accent or a larger part?)
There are two reason why the Shulchan Aruch Y:D writes why not to wear red clothing, because it was the custom of the gentile to dress this way, and because the color red lends itself to haughtiness and promiscuity, (in contrast to the color black which gives off a different impression). The poskim write that this only applies to a garment that is actually red , but not to clothing that is wine colored etc. Additionally, it only applies if the whole or most of the garment is red, but not if it only has a little bit of red in it.
Rema Y:D 178-1, Halichos Bas Yisroel 7-3 in name of R’ Eliyashiv zt”l.