In this Wikipedia article it gives a bunch of X11 colours but they are different from the ones on my FreeBSD system. For example I have no "aqua" or "fuchsia" but, e.g. aquamarine1, etc. and many other numbered colours. Why is that?
I use this page as color reference when looking for an X11 color:
The article explains it pretty well
These charts are not a standard set of colors to be found on any X Window system. Rather it is the standardised "X11 colors" accepted by browsers following the HTML and CSS standards. This set is cut down and rationalised, and has a few differences from a typical rgb.txt...