Lab model
The CIE L*a*b* color model (Lab) is based on the human perception of color. It is one of several color models produced by the Commission Internationale d'Eclairage (CIE), an organization dedicated to creating standards for all aspects of light.
The numeric values in Lab describe all the colors that a person with normal vision sees. Because Lab describes how a color looks rather than how much of a particular colorant is needed for a device (such as a monitor, desktop printer, or digital camera) to produce colors, Lab is considered to be a device-independent color model. Color management systems use Lab as a color reference to predictably transform a color from one color space to another color space.
Lab describes color in terms of luminance or its lightness component (L) and two chromatic components: the a component (green and red) and the b component (blue and yellow).
Photoshop uses Lab as a color reference in color management and lets you work in Lab Color mode.
In the Adobe Color Picker, select a color in RGB, HSB, or CMYK mode to see the related numeric values in Lab. (See Using the Adobe Color Picker.)