Also: Gap has a special approach to “seasonal” colors. Because they sell their own clothes, and because all of the mall chains adopt basically the same palette at once (when the new season’s colors come out), most stores try to pick clothes that will match well with almost anything else bought that season. Gap clothing always uses hues and tones of the hot colors that are just slightly different, so that a Gap T-shirt will clash if you layer it with anything else seasonal – unless that “anything else” was also bought at Gap.
I have a pair of grey cargo pants that looked great when I bought them (because my wardrobe happened to be “in season”) but manage to look bad with anything but pure black or white shirts. The grey has green undertones that cause it to clash horribly with pretty much any color except the other neutral tones Gap was selling that year.