I would say that an accurate maintenance history and condition would be the most important factors. Be aware of some of the common problems so you'll know what to look for (i.e. intake manifold gasket, rear rotors, windows, cv boots on lifted VXes, etc).

In general, newer with lower mileage is better, but you should be especially attentive when inspecting any vehicle that sat undriven for a long period of time.

I'm not sure that there is any consensus on which is the preferred color. I'm personally not a fan of the Proton - I like the Ebony and the Ironman the best. If you are worried about resale value, you may want to reconsider and buy a Honda Accord.