Not sure how much you're kidding, but... that's true for a subtractive colour system, where you start with a white sheet of paper (i.e. reflects every wavelength) and subtract colours (filter out wavelengths) by painting over the paper with crayons. For an additive colour system, where you start with a black monitor screen, and you add wavelengths, the primaries are RGB.
...and, strictly speaking, the subtractive colors that closest match the typical human eye are cyan, magenta, and yellow -- the "CMY" of CMYK printer inks. Using red, yellow, and blue as subtractive colors gets you a big enough gamut for elementary school color mixing, but it won't give you as big a range of colors as CMY.
