I have to disagree here, not with the fact that coloring makes things more colorful (lol) but just the fact that OP seems to be going for a manga, screentone style, and adding color might just not be within their stylization choice.
Ex:
Working without color can work, you just need to know how to differentiate foreground from background and objects apart from one another using different shades of black, grey, and white. In this case, OP would probably benefit more from learning how to do so, either through shading or just adding more greyscale to the objects in the world.