Most of my body hair is black however my lip hair is light brown/blonde the rest of my beard region is black. Since hair color is genetic what causes this?
The hairs you mention are also called "androgenic hairs", meaning their growth and pigmentation is influenced by androgens. These include pubic hair, the hairs on the breast and shoulders (almost exclusively for men) and the beard.
It seems, that these hair bulbs have different sensibilities (number and expression of androgen receptors) so they react differently to androgen levels. This includes balding, pigmentation, growth and so on.
These articles should be a good starting point, if you want to dive deeper into the topic:
I've heard it mentioned that gene dosage is implicated in this. Gene dosage is the number of the alleles present in the cell.