This question is depicting a phenomenon in inheritance called CODOMINANCE, which is a type of non-mendelian inheritance in which two alleles of a gene both express themselves in that gene. In this question, the allele for blue color (B) is codominant with the allele for yellow color (Y).
This means that an individual that has a blue phenotype will possess the genotype BB while an individual that has a yellow phenotype will possess the genotype YY. Hence, in an heterozygous state in which both alleles combine to produce a simultaneous blue and yellow phenotype, the genotype will be BY or YB.
