Shading and blending :) Wait for first layer to dry basic color , than add darker tone for shading and start from edges, from darkest part, and than try to add more water as you go down* like melting*. I hope you will understand written, I am much better with painting than with words :)
Ohhh I am so lucky to get a tip from you <3.
I will try to apply it, thank you very much Dunja ^_^.
Though sometimes the paper disagrees with me if I introduce too much water. It is hard but quite fun :D.