Learn to do other things with your lines so you can get rid of them. Right now you use them to divide sections of you art so it shows shapes.
On a side with shadows it is fine for the lines to be black, because that side is shaded anyway. When there is a side light only hitting on side of the shape it is better if it is the color of that light. If you take out lines then you need to replace them with light and shaded areas.
It looks like your art is heading away from lines, so at some time you might want to start drawing silhouettes and drawing details or draw details until they show you where the edges are. Both ways work, but the second way would be quicker.