I also agree the contrast range needs to be expanded; it’s too narrow. Go extreme, go over the top. Push past your comfort zone; break it. Break it hard. I’d rather you have a wide range and know when to pull back than to try and push past your narrow range.
I also suggest taking a look into Hue Shifting, especially for things like skin tones. While adding black and white can certainly increase your contrast, it makes your skin tones look muddy and dull. This is just not how we perceive the world (exceptions, of course). I also suggest picking up this book, which talks about how color and light interact. Are you sure those shadows are black, or are they just slightly blue? Go outside at different times of day and do some studies. You’ll be surprised how color changes based on light.
Here’s an extreme example of hue shifting for skin tones. The light is towards the yellow-orange while the shades of the skin are bluish-purple. What effect does this have on the character? How can you match this with your own work? Analyze it, then apply it to your own work. Work on your observation and analytical skills and apply what you learned. Keep experimenting. You got this.
