Answer:
The correct answer is - incomplete dominance.
Step-by-step explanation:
Incomplete dominance is a type of inheritance in which the dominant allele or gene does not mask the other gene or allele completely and produce a blend or mixture of both alleles in the phenotype.
In this case, where alleles are in their pure breed they show their respective yellow and blue color but after the cross, they produce offspring with the heterozygous condition, and due to incomplete dominance they produce a mixture of both alleles in the offspring.