What about Red, Yellow and Blue?

Paint and crayons work by subtracting colours. So, the primary colours for paint and crayons are the subtractive primaries, yellow, cyan and magenta. (For example, yellow works by taking the blue away from white light.)

 Cyan  and  magenta  look like shades of  blue  and  red , so they are sometimes called simply that - blue and red.

That's why many people list the subtractive primaries as red, yellow and blue. The subtractive primary "blue" is really a particular shade of light greenish-blue, called cyan; and the subtractive primary "red" is a light purplish-red, called magenta.