I kinda have a bit of a color wheel in mind! I try to make whatever's the major color on a character as close to a nice, vibrant but not eye-burningly saturated, deep blue-violet. Then, I try to match/adjust based on that. Generally, purples and blues will get bluish-purple, pinks and whites become purple, yellow and orange probably more magenta-ish, greens become blue/teal, and like... basically I try and just keep those close to the main, prominent deep blue-violet bc that IS the color of blueberries! I try and stray away from berries that are too purple, or too pure-blue