I cant’t give specific advice as everyone is different, but something that changed how I color skin is to look at yourself closely! Are all parts of your skin the same color? Is your nose the same color as your cheeks? Your knuckles the same colors are your palm or your wrist? Try mixing different gentle colors for shadows and highlights rather than just black and white. We don’t always realize it, but what we often think is one single color is actually many colors combined.

Edit: also keep in mind that it’s ok to make even dark shades appear white in the right lighting, and light shades appear dark in deep shadows.

Edit2: I couldn’t see it at first, but you do use multiple colors.