in my dreams, the F1 has always been a silver/gunmetal type color. but hey, thats just me.
if ur getting a McLaren, dont limite ur ideas to just basic colors (blue, red, yellow, black, etc.). try going the DK way and have a shifting orange paintjob. the XP4 looks great in blue, but its been done already. personally, i believe that each McLaren should have a distinct color that makes it easier to identify over other F1 cars.
if u can find someone who knows how to do it, try getting the "MystiChrome" paint that is seen on the special edition Ford vehicles. it would MOST DEFINANTLEY set ur car apart from the others. the only problem with MystiChrome is that only the people at Ford know how to do it so its going to be difficult to find someone that can.
also, i always kinda liked a dark purple color. i dont know if its already been done, i havent seen any pics.
here r some pics of a MystiChrome Cobra Mustang. notice how the shifting colors as the camera takes shots from different angles:
