Difficult decision.
Blue: Looks beautiful on the R32, classic for the car, unique to the R32 within the model but I think there are more blue R32s than other colors.. Not so unique within the street racer category as STI, EVOs etc have a similar color.
White: The new silver. Popular choice, looks great, can't go wrong. Nice to mod.
Grey: Sportscar tradition in the Bmer style. Suit and tie and red condoms. Safe choice. Maybe too safe depending on your personality.
Red: Under rated. Beautiful color and looks hot when modded.
Silver: Yesterday's news. Not enough statement for the R32. Over done on other sportscars.
Use your indecision to your advantage. Choose a color as if it is your only choice for a car which the dealer doesn't have on the lot and work them for a good deal. Target a car they will have to bring in. (This will also make you feel like you have made the choice and the color remorse demons will either appear or not.) Then when you are close to a deal but not over the edge mention you sorta like the other color on the lot. The dealer should be incented to move a lot car especially in a slow market. You can't go wrong with any of these colors and may save some money.