I'm told the red reaches it's max by 2 years old. When River was born she looked black and white, within 3 days the brown started appearing, when she was 3 weeks old she clearly was a different color than her sable sisters, and by 4 months her blanket pattern appeared. Between 1 year and 2 years is when she really got red.
eta: I've got no color bias. I love a pretty papillon, no matter what the color or pattern. So I have 3 colors of the spectrum bouncing around here.