A little trivia about the color magenta: while most of us were taught as children that the primary colors are red, yellow, and blue, the actual primaries are really cyan, yellow, and magenta.
You're right, there's apparently a good case to be made for cyan, magenta, and yellow (instead of blue, red, and yellow) as the primary colors for pigment (e.g., ink, paint, and crayons). When you make colors using lights, however (e.g., a color computer monitor, or colored spotlights on a stage), the primaries are generally considered to be red, green, and blue.
The reason that there are generally considered to be three
primary colors is that most humans' eyes are the most sensitive at three points in the color spectrum. For other species (as well as some humans) there may be two or four primary colors. Here's an interesting write-up from Wikipedia
Now, please excuse my poor memory, but where does "magenta" enter into this episode?