Well 5 colors for 16x is like the perfect amount of shading imo, but the 3 colors for the 32x one is so that I can practice things like shape and rendering different materials at a more basic level. The shading could just come natural afterwards, but limiting yourself to midtones, highlights, and shadows helps you better understand the textures and how lighting affects them. And I like the challenge I dunno it seems more interesting to work with limitations. It kind of creates a nice style imo.