CSS also has many properties that can be set to a color, i.e. color, background-color, border-color, box-shadow, etc. Colors consist of three or four values corresponding to the amount of red, green, and blue light blended to create the color. The optional fourth value is the alpha, and is typically used to specify transparency.

Colors are stored as 24-bit values, with 8 bits for each of the four channels (R,G,B,and A), representing 256 possible values (2^8) for each channel.

Colors can be specified in one of several ways:

• Color Keywords like red, dark-gray, chartreuse correspond to well-defined values. You can find the full list in the MDN Documentation.

• Hexidecimal Values like #6495ed, which corresponds to cornflower blue. The first two places represent the red component, the second the green, and the third the blue. If an additional two places are provided the last pair represents the alpha component. Each pair of hex values can represent 256 possible values (16^2), and is converted directly to the binary color representation in memory.

• RGB Function a third option is to use the RGB() CSS function. This take decimal arguments for each channel which should be in the range 0-255

• HSL Function a fourth option is the HSL() function, which specifies colors in terms of an alternative scheme of hue, saturation, and lightness.

• RGBA and HSLA Functions finally, the RGBA() and HSLA() functions take the same arguments as their siblings, plus a value for the alpha channel between 0 and 1. This alpha channel represents the opacity/transparency of the color, with 0 being fully transparent and 1 being fully opaque. Thus, a value of .75 represents 3/4 opacity, or 1/4 transparency.