hii! first off your art style is GORGEOUS! i don’t do realism as well as you, but here’s some general colouring tips i’ve learnt that could help you :))
-don’t be afraid to make your shadows darker!! and play around with layer blend modes as skin can have many different tints to it! (example that i use: multiply, light purple, lower opacity for dark shadows!)
-avoid using the airbrush, gives a very foggy look. try using more hard brushes and edges to your drawings! afterwards, you can touch up by using blurring/airbrushing for points where the shadows are softer.
-avoid using the colour white at all costs. try using a more off-white colour for both the skin and the eye whites. same thing for pure black.
-more on shadows: try to avoid just lowering the brightness, adjust the hue to a warmer colour and adjust the saturation to what seems better (test around!)
-watch. tons. of. speedpaints. see what technique they use, and try using them onto your pieces! also watch tons of tutorials :))
otherwise, i really hope this helps! i can’t wait to see more from you; this is great for a beginner!