Your book is correct; shading is not just using black and white to lighten or darken your colors. For instance red can be shaded using yellow, green, blue, or other colors depending on what you are trying to achieve. You need to understand the color wheel and complementary colors to learn and understand shading highlighting. Shep Paine's "Building and Painting Scale Figures" has an excellent chapters on color and basic shading, if you can lay hands on a copy (it may be out of print). Another excellent book is 1500 Color Mixing Recipes by William F. Powell. I got my copy of this one at Barnes and Noble. Color is a complicated subject (at least for me) and not easy to explain in a few sentences or paragraphs. I'm still learning. Practice blending colors and prepare color cards to catalog your mixes, so you can refer to them in the future (I guarantee that you will forget mixes that worked if you don't keep some kind of reference). Hope this helps.