Interesting way he counts the colors. Makes sense though, after some thought. Specifics: slide 34. Formula is (each item is a number of colors): fill + text

Interesting way he counts the colors. Makes sense though, after some thought. Specifics: slide 34. Formula is (each item is a number of colors): fill + text + lines - background The minimal number would be 2, with text=1, background=1, and no lines and filled shapes. That is the case with pure text slides, typically B&W. When we draw lines and fill shapes, we may introduce additional colors, or what feels as adding colors to a purely B&W picture. We could also have portions of text and/or background color-coded. In any case, the author apparently counts the number of additional colors. He suggests the number should be small (no more than 3, see slide 35), in order for the viewer to keep the "color coding" manageable.