Alpha (alpha channel)

The alpha channel specifies the opacity of a <color>. Colors are represented in digital form as a collection of numbers, each representing the strength or intensity level of a given component of the color. Each of these components is called a channel. In a typical image file, the color channels describe how much red, green, and blue are used to make up the final color. To represent a color through which the background can be seen to some extent, a fourth channel is added to the color: the alpha channel.

For example, the color #8921F2 (also described as rgb(137 33 242) or hsl(270 89% 54)) is a nice shade of purple. Below you see a small box of that color in the top-left corner and a box of the same color but with an alpha channel set at 50% (or 0.5) opacity, #8921F280, where 80 is the hexadecimal equivalent of 50%. This color is also described as rgb(137 33 242 / 50%) or hsl(270 89% 54 / 50%). The two boxes are drawn on top of a paragraph of text.