Strains of petunias come in four pure-breeding colors: white, blue, red, and purple. White petunias are produced when plants synthesize no flower pigment. Blue petunias and red petunias are produced when plants synthesize blue or red pigment only. Purple petunias are produced in plants that synthesize both red and blue pigment (the mixture of red and blue makes purple). Flower-color pigments are synthesized by gene action in two separate pigment-producing biochemical pathways. Pathway I contains gene A that produces an enzyme to catalyze conversion of a colorless pigment designated  to blue pigment. In Pathway II, the enzymatic product of gene B converts the colorless pigment designated  to red pigment. The two genes assort independently.

What are the possible genotype(s) for true-breeding blue petunias?