Blue is one of the primary colors of light. It's a primary color in additive color mixing and a secondary color in subtractive color mixing (the product of cyan and magenta). Pure blue light has a wavelength of approximately 436nm. Blue light accounts for 11% of the perceived brightness of an object.

Subtractive (printed) blue	Additive (computer screen) blue

Blue is a cool color, instilling peace, tranquility and sobriety. Darker shades can lead to sadness and depression. Blue also symbolizes wisdom, loyalty, and dedication. Blue rooms can increase productivity, and information retention increases when text is printed in blue. However, blue cones are the least numerous in the eye, leading to lower visual accuity than for red or green. Blue text against a white background is easier to read than against a black background. Blue is an extreme appetite supressent, as virtually no food in nature is blue.