Color in CSS→

Ars Technica:

By 2001, the World Wide Web Consortium (W3C) published the first working draft of the CSS 3 Color Module that would include the colors. In light of evolving technologies, the colors had fallen out of use, but the W3C claimed the goal was to “codify current practices.” Every browser supported the colors at this point, consequently, the W3C had been using them in compatibility tests. Incorporating the colors into CSS, then, would prevent sites from breaking.
“It was like a backwards-compatibility thing. They thought, ‘We’ve accidentally been doing this, so we might as well just not break it,’” Sexton told Ars.

“We’ve accidentally been doing this, so we might as well just not break it” is, if I do say so myself, a great way to describe the inclusion of a lot of the features that users of the modern web take for granted. Though we like to pretend that HTML5 and CSS3 were the result of a lot of planning, they were mostly playing catch-up to what web developers and the browsers were already doing.