I tend to prefer uncommon colors; bama clay and desert sand are both pluses for me. As P-Easy noted, Tanker has been a very popular color for the last year or so (more so than the previous [lighter] gray they called Urban) -- I bought all Moss and Tankers in this order.

I'm not sure that any particular blade color sells more quickly or for more money on the secondary market; most buyers consider one coated blade about the same as any another. Some handles, like snake skin Micarta, add to a knife's value though. Paper Micarta used to sell for a premium, but now that it's a standard handle option, that probably won't continue.