Hex colors: Numeric representation for “transparent”?

Question

I am building a web CMS in which the user can choose colours for certain site elements. I would like to convert all colour values to hex to avoid any further formatting hass

Answer 1

The alpha channel defines the transparency value of a color, so any color is 100% transparent as long as the alpha value is 0. Typically this four-channel color type is known as RGBA.

You can specify RGBA in CSS like so:

div {
    background: rgba(200, 54, 54, 0.5); /* 50% transparent */
}

Note that not all browsers support RGBA, in which case you can specify a fallback:

div {
    background: rgb(200, 54, 54); /* fallback */
    background: rgba(200, 54, 54, 0.5); /* 50% transparent */
}

More information regarding browser support and workarounds can be found here.