If skin color were inherited in a simple dominant or recessive pattern, like seed color in pea plants. What would be the genotypes of dark- skinned parents that could produce fair-skinned children?

the genotypes of both parent would have been heterozygous for the trait.

Explanation:

In the simple dominant or recessive pattern as described by Gregor Mendel  in the year 1865 involving single gene inheritance. Illustrating this pattern using dark-skinned and fair-skinned people. Assuming dark-skinned to be dominant over fair skinned. the dark skinned parents if both are homozygous for dark skinned would not produce a fair-skinned child but if both are heterozygous for dark skinned, a fair skinned child can be produced. using D to indicte dark-skinned and d to indicate fair skinned, we have:

genotype       DD           x            DD

F1 genotype                 DD

phenotype             dark skinned

genotype              Dd            x           Dd

F1 genotype          DD      Dd                dd

phenotype         dark skinned and fair-skinned

i'd have to say the answer is probable the second option "the geosphere interacting with the atmosphere"