Final answer:
When two individuals with the same genotype for a trait display different phenotypes for that trait, it suggests incomplete dominance, codominance, or other factors influencing gene expression like environmental influences or epigenetics.
Step-by-step explanation:
If two individuals have the same genotype that codes for blue coloration but only one of them presents blue coloration then the trait shows incomplete dominance or codominance.
Two alleles for a given gene in a diploid organism are expressed and interact to produce physical characteristics, with the observable traits expressed by an organism referred to as its phenotype. An organism's underlying genetic makeup, which alleles it has, is called its genotype. In the case of incomplete dominance, the heterozygote presents a blend of traits from the two alleles, like pink flowers resulting from one allele coding for red and one allele for white. In the case of codominance, both alleles are simultaneously expressed, such as the MN blood groups in humans, where both M and N antigens are present on the surface of red blood cells in heterozygotes.
Since the two individuals have the same genotype for blue color but exhibit different phenotypes, it suggests that the expression of the trait is affected by factors like incomplete dominance or another form of genetic interaction such as environmental factors or epigenetics that affect gene expression without altering the genetic code.