Factors A, B, C, D control the production of a black pigment. The genes encoding A, B, C and D are independently assorting. The alternate alleles that give abnormal function of these genes are a, b, c, and d. A black AA BB CC DD is crossed with a colorless aa bb cc dd to give a black F1. The F1 is then backcrossed with a colorless aa bb cc dd. Assume that A, B, C and D act in a pathway as follows:
A B C D
colorless → colorless → grey → brown → black

What percentage of the F2 are brown?
A. 1/4
B. 1/6
C. 1/8
D. 1/16
E. None of above