Here is the code for the race picker. 1-4 are white races.
Basically, 1 in 3 chance to pick from all races (including white), and 2 in 3 chance to pick only a white race.
So far from what I see, either any darker than white rice is seen as black, or just any amount of dark tones are unacceptable. But generally a dark tone has much less than 1 in 3 chance of showing up.
Python:
if not numgen(0,2):
npc_race = numgen(1,10)
else:
npc_race = numgen(1,4)
So far from what I see, either any darker than white rice is seen as black, or just any amount of dark tones are unacceptable. But generally a dark tone has much less than 1 in 3 chance of showing up.