So I was doing a bit of research on skin colors via location and factors + melanin for the characters of Dragon Quest Builders 2; here's my conclusions.
Furrowfield - Mild UV radiation + consistent sun exposure; the people are more often than not tan-skinned due to how often they stay in the sun, although the radiation is not enough to require high levels of skin-protecting eumelanin.
Khrumbldun - High UV radiation + semi-consistent sun exposure; the people are darker-skinned due to needing to produce more skin-protecting eumelanin, although the miners are paler due to less sun exposure.
Moonbrooke - Low UV radiation + low sun exposure; the people here are living in almost constant snowstorms and there would not be much sunlight, leading to them being almost as/as pale as the snow they're surrounded by.
(to anyone more experienced possibly reading this; feel free to correct me on any of this as I am learning and not an expert!)