RGBA color model

The RGBA color model represents color with red, green, and blue components plus alpha, which encodes opacity or transparency.

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RGB color model: An additive color model that represents colors through red, green, and blue components. RGBA extends RGB by adding a channel for opacity or transparency.
Alpha channel: A digital image channel that stores opacity or transparency information for pixels. It is the additional channel that distinguishes RGBA from RGB.
CSS color: A set of web-platform specifications and syntax for representing and manipulating colors. CSS accepts color values with alpha for translucent interface elements.
Indexed color: A color representation in which pixels store indices into a palette of colors. It encodes pixels through palette references rather than direct RGBA channel values.
Alpha compositing: A method for combining foreground and background colors using opacity values. It defines how RGBA alpha affects the displayed result.
Source-over compositing: A compositing operation that places a source image over a destination using source opacity. It is the common rule for applying RGBA pixels over an existing image.
Canvas API: A browser API for drawing and manipulating two-dimensional graphics in a canvas element. Canvas image data commonly exposes pixels as RGBA channel values.
CMYK color model: A subtractive color model based on cyan, magenta, yellow, and black ink components. CMYK describes print colorants, unlike RGBA's additive display channels and alpha.
Color depth: The number of bits used to represent the color of a pixel. Bit allocation determines how precisely RGBA channels can be encoded.
sRGB: A standardized RGB color space and transfer function used widely in digital imaging. Many RGBA values use sRGB channel encoding rather than linear-light values.