Actually - the majority of Japanese R33 GTRs (and other cars) are white - as it is seen to be a lucky colour...
Anyhoo: colours like white, silver and black are 'traditional' colours - and tend to be popular no matter what the current market trend is. These are factory R33 GTR colours:
AN0 Super Clear Red
BN6 Deep Marine Blue
KH3 Black
KL0 Spark Silver
KN6 Dark Grey
LP2 Midnight Purple
QM1 White
KP4 Sonic Silver
AR1 Super Clear Red 2
The deep marine blue is rare, as is purple (unless you live in Melbourne, where it seems, everyone has a f*cking purple one ) I have never seen a red one though. Championship blue was only available on the LM special edition.
The purple was the R33 GTR 'signature' colour (gunmetal grey for 32, bayside blue for 34). And it sure is pretty - see my photo links for example
There is no easy answer as to why the above colours were chosen (some are quite complex - the red and purple are both pearl) - market trends, advertising arrangements, personal preference - who knows? Recall in the early 90's, all the euros (Benz, BMW, VW, Volvo, Opel etc) produced cars in a pastel yellow (think Taxi) which may have been cool then... but sure looks crappy now.