The minimap has 2 colours as stated on the Display>Interface menu:
Small map dark
Small map light
IIRC Small map dark is only used when in 3rd person, and small map dark is used on the rest of views, because of, for example, car interiors where they are mostly black (except cars with no roof, like RAC, UF1 roofless and both LXs) because they would camouflage with the texture and be like there is no minimap, if using minimap on total black colour, or where some tracks have dark spots, or dark textures itself.
Also I know there is a bug on both Display and Interface sliders where they show incorrect colours when moving them (like, you want to make orange and it shows purple or dark green and etc). I think the Interface tab doesn't have this problem, but may be wrong.
Do both minimaps have the same colour? idk if you know the trick, but you can use ctrl+LeftClick to copy and Shift+LeftClick to paste sliders value.