You are correct about the additive primary colors, red, green, and blue. For reflected light the subtractive primary colors are magenta, cyan, and yellow. These are the colors of the inks in your color printer. Each of these primary colors subtracts or absorbs one of the additive primary colors. Cyan absorbs red (reflecting green and blue, which combine to be seen as cyan). Magenta absorbs green and yellow absorbs blue. So to get blue, for example, reflected from your printed page, you must subtract red and green, so the printer combines both cyan and magenta pigments. When all three subtractive primary colors are combined, all additive primary colors are absorbed (red, green, blue) and we see nothing reflected back (i.e. black).