There are three primary colours (of light): red, green and blue. Any two of these colours can be mixed to give a secondary colour as follows:
Red + Green = Yellow
Red + Blue = Magenta (pink)
Green + Blue = Cyan (Turquiouse)
If all three colours are mixed together, white light can be obtained.
Note that these are the primary and secondary colours of light. The primary and secondary colours of pigment (paint) are not the same.