Final answer:
The trait indicated by the green color being expressed in individuals is likely a result of a recessive allele, which is only visible when an individual is homozygous for that trait.
Step-by-step explanation:
In the given scenario, where the green color trait is being expressed, it suggests that this is a phenotype that is visible. If we take the lessons from Mendel's genetics, particularly regarding pea plant coloration, we understand that if the green color is expressed in the absence of the yellow dominant trait, it is very likely that the expressed green color trait is due to a recessive allele. This is consistent with our understanding of inheritance patterns where a dominant allele overshadows the presence of a recessive allele in a heterozygous individual, resulting in the dominant phenotype being expressed. However, for the recessive green trait to be visible, the individual must be homozygous for the recessive allele (possessing two copies of said allele).