First he becomes pale with anger, but after Lizzy says, "Had not my own feelings decided against you -- had they been indifferent, or had they even been favourable, do you think that any consideration would tempt me to accept the man who has been the means of ruining, perhaps for ever, the happiness of a most beloved sister?" Darcy changed colour. And later:

"You take an eager interest in that gentleman's concerns," said Darcy, in a less tranquil tone, and with a heightened colour."

So I still don't think we can say for sure whether Darcy turned white or red on seeing Wickham.