In your scenario, the dominant alleles A and B represent color traits, while the recessive alleles (a and b) will mask the expression of color traits when present together in aabb genotype.
Given that aabb is a recessive genotype, and typically recessive traits may correspond to a specific color (in this case, white is a common representation of a recessive trait for dogs), the response that would be correct according to typical Mendelian genetics would be:
aabb, White