Aqua is a tone of the color cyan (from Greek: κύανoς (transliterated: kýanos), meaning "blue") which is identical to the color electric cyan, one of the three secondary colors (subtractive primary colors) of the HSV color wheel, along with magenta and yellow. It is precisely halfway between green and blue on the color wheel. It should not be confused with the color process cyan used in printing, which is a deeper tone of cyan; this color is also known as deep aqua.

In traditional print media, "aqua" is short for aquamarine, a distinct color from aqua. The words "aqua" and "cyan" are used interchangeably in computer graphics, and especially web design, to refer to the subtractive primary color "electric cyan". Traditionally that color, defined as #00FFFF in hex, or (0,255,255) in RGB, is called "cyan", but X11 color names introduced the alternative name "aqua". Later, W3C popularized the name by using it in the named color palette of HTML 3.2 specifications.

Displayed at right is the color pale aqua.

Aqua is the Latin word for water. In English, it may refer to:

Color or colour (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, green, blue, and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates.

Because perception of color stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully explain the psychophysical perception of color appearance.