Sometimes I take inspiration from existing color palettes on sites like coolors.co for both character designs and artwork :] If I'm making color palettes from the ground up I usually think about color theory rules, most of the time though I just slap my favorite colors together. More often than not I try to make each color as distinct from each other as possible (at least one light, one dark, and one middle). It also depends on the character design and the vibe of the artwork that I wanna go for!