I have a silver K4 but like the post above wasn't reg'd til 2005. If you paint a black frame silver you'd better be keeping it for life you'll lose times more on your resale value as what it will cost you to have it done. (making it look 2 years older - no one will accept any explanation of why you wanted to do that!)
Buy new - at least you'll know it's history.

Changed my mind
 

Thanks for your comments. I think the black frame only looks nice fully faired in yellow, but I've searched high and low and can't find one anywhere (I believe they did the K5 in Yellow, but not the K6???). I wanted to get a brand new bike for piece of mind, as i've had bad experiences of buying 2nd hand cars where the previous owner has messed around with things and made the vehicle dangerous. This will be my 1st bike so I want to make sure it won't fall apart on me! I'v seen a K4 fully faired in yellow which looks pretty tidy so i'll probably go for that, but take a mechanic with me to check it out fully before buying it.