Blue/White will always be THE classic GTS color. When I am around a group of Vipers, my eye is still drawn to the Blue/White even though I have a yellow one myself. Of course Red is the classic color on the RT/10, though it is also a fairly common color. Past that, I think some of the better looking low production number colors like Graphite which are only offered for 1 year will hold their value better than some of the more vanilla colors like red that span multiple years. Basic law of supply and demand.