The three primary colors, red, yellow and blue, are the only colors that cannot be created by mixing other colors. Blue mixed with red makes purple, blue mixed with yellow makes green and yellow mixed with red makes orange. read more
For printing inks, transparent paint, color filters or other subtractive light process, the colors cyan (= minus red) and magenta (= minus yellow) make blue. For more information see, for example, the CMYK color model on Wikipedia. read more