Once at a job when I was supposed to make a website work (and I'll stress, I am not a graphic designer and wasn't hired as one!) I made the layout as nice as I could, but I insisted on only using named CSS colors because I just do. not. care. about color theory. By which I mean, I don't want to waste time and do a crappy job at it when someone else could do it much better and properly and faster. So the named colors are meant as an obvious placeholder for a more creative person to replace with something real later.

When my boss gave me feedback he just said that it's ugly. I started saying "yeah, the colors are placeholders, we can change that easily. I'll fiddle it with it I'll stick with named colors" (above explanation was to follow).

Before I even got to the named colors bit, he interrupted me and said "don't use named colors ever".

I guess maybe I was hired as a graphic designer? News to me!

(I'm making him sound awful but he was actually a really good boss. This interaction is not representative of our usual dynamics. I'm not employed by him anymore but we are on good terms.)

X11.

One notable difference between X11 and W3C is the case of "Gray" and its variants. In HTML, "Gray" is specifically reserved for the 128 triplet (50% gray). However, in X11, "gray" was assigned to the 190 triplet (74.5%), which is close to W3C "Silver" at 192 (75.3%), and had "Light Gray" at 211 (83%) and "Dark Gray" at 169 (66%) counterparts. As a result, the combined CSS 3.0 color list that prevails on the web today produces "Dark Gray" as a significantly lighter tone than plain "Gray", because "Dark Gray" was descended from X11 – for it did not exist in HTML nor CSS level 1 – while "Gray" was descended from HTML. Even in the current draft for CSS 4.0, dark gray continues to be a lighter shade than gray. Some browsers such as Netscape Navigator insisted on an "a" in any "Gray" except for "Light Grey".

I literally only use them when testing.