I think I know what you mean, Gino. We often talk about highlight, midtone, and shadow colors but it's a spectrum, we're really just referring to lighter or darker shades. In an area that's lit (where you're using mostly highlight colors), you can still have shadows but maybe they're created with a mix of midtone and highlight instead of the actual shadow color. And, while you may not have true highlights in a shaded area, you still have sections that are relatively lighter. It's just whether or not this shade darker or lighter than the surrounding color. We can get into all sorts of complexities of light and shadow... ambient light vs direct light, occulsion shadows, etc.