Mixing red and blue together makes the color purple. Red and blue are primary colors, meaning they cannot be created by mixing two other colors, and purple is a secondary color, meaning it is created by mixing two primary colors.
An artist can achieve different hues of purple depending on the ratio of the colors mixed. Mixing a large amount of red and only a little blue makes a magenta shade of purple. Mixing a large amount of blue and only a little red makes a violet shade.
Yellow is the color opposite purple on the color wheel, so purple and yellow are considered to be complementary colors.