The color range of display is defined by the term color depth. The amount of color associated with each pixel on the display screen is called color depth. Displays use the red-green-blue (RGB) additive color model. The RGB model is called "additive" because a combination of the three pure colors red, green, and blue "adds up" to white light. The most common color depths are 8-bit (256 colors), 16-bit (65,536 colors) and 24-bit (16.7 million colors).
8-bit color ( 256K ) : Uses one 8-bit byte per pixel and 256 colors can be represented in the color palette. Various graphics formats are limited to 256 colors; there are 3 bits (8 possible levels) for each of the R and G components. The normal human eye is less sensitive to the blue component than to the red or green, so it is assigned one bit less than the others.
16-bit color (65K ) : Uses two bytes per pixel and 65,536 colors can be represented in the color palette. It supports 16-bit for three RGB colors. In 16-bit direct color, there can be 4 bits (16 possible levels) for each of the R, G, and B components, plus optionally 4 bits for alpha (transparency), enabling 4,096 (16 × 16 × 16) different colors with 16 levels of transparency.
15-bit color (56K ): Uses two bytes per pixel and one bit of two byte is ignored for alpha channel. Usually the color is represented by 15 bits.
24-bit color ( 16M ) : 24 bit color also known as True color supports 24-bit for three RGB colors. For each pixel, generally one byte is used for each channel while the fourth byte is being used either as an alpha channel, data, or simply ignored. It provides a method of representing RGB color space in a very large number of colors, shades, and hues. It requires three times as much memory, disk space and processing time to store and manipulate 24-bit color images.