Jeremy,
Back in the day when Speedsters were new, silver was the German racing color. (Brits painted their cars BRG, Italians wore red, US cars were blue, etc.)
My Speedster is a Porsche silver with a red interior and it got lots of attention and compliments when I showed it last Spring. My Spyder is the same color combination.
It's certainly one of the most popular combinations for these cars. I think re-sale would be adversely affected by a non-standard color combination like a metal flake or pearlescent. But, again, lots of guys build their cars to their personal tastes and forget re-sale. Best advice is to choose a color combination that you like that may have been offered originally by Dr. P's company.
Jim
ProSpyder