A common misunderstanding when we’re putting one color on top of another is that it’s being layered on top of the old one. In reality, rather than just overlapping it’s being blended into the existing tattoo pigments. The two colors both remain in the skin, mix, and alter the color you're putting in. The same goes for tattooing over black as well. Any color you add will blend with the black tattoo pigments and be shaded respectively.
Another tip that may not seem that important is using a variety of the same color in your piece. Instead of just tinting the color darker or lighter with black, try muting the color with it’s complementary or changing its temperature to slightly warmer or cooler. These small changes will greatly affect the entire outcome of the piece and make a noticeable difference in creating depth.