Lavender is a light value of the tertiary color red-violet, so it is made of shades of red and blue. Specifically, lavender has more red than blue. It also includes some white to create the tint.
Lavender is classified as a cool color because of its blue base. It is tertiary because it is not an exact mix of red and blue, which would be a the secondary color violet, also frequently called purple. Lavender instead falls between prime red and secondary violet. The color gained its name from the flower of the same name. The exact hue is usually taken from the lightest part of the flower.