Magic

Susceptor people have the ability to wield magic. Magical ability is determined by a single recessive gene with many alleles, which are co-dominant. This means that magic can be 'bred out' of a population or can skip a generation when Susceptor interbreed with non-magical peoples. It also means that susceptor can have one, or two powers at once, depending on what is inherited from their parents.   There are twelve branches of magic. The magic a susceptor has will determine their skin colour. For example, a user of shadow magic, Umbra, would have violet skin. In cases where a child is born with two magical powers, they are both expressed on the skin, in swirling patterns aligning with the Blaschko's lines.