Epistasis is occuring, leading the albino locus to mask the action of the black/brown locus in some individuals. This causes a modified ratio.
Work Step by Step
Whenever a ratio doesn't match the simple, expected Menedelian genetic ratio, such as 9:3:3:1 in this case, some non-Mendelian phenomenon must be occurring. In this case, one locus is affecting the other, essentially pushing the second 3 in the list of probabilities into the double homozygous(albino)-produced phenotype.