CSS color values can take one of several forms.
This page's body is set to color: white; background-color: black;
This paragraph is set to color: #f83333; background-color: #444;
This paragraph is set to color: rgb(0,127,255); background-color: rgba(0%,50%,50%,0.5);
This paragraph is set to color: hsl(240,100%,75%); background-color: hsla(0,0%,100%,0.2);