Clashes between web and X11 colors in the CSS color scheme (en.wikipedia.org)

The definition of grey is totally debatable, but in W3C spec Green = #008000 (instead of #00FF00, which is called Lime?) makes no sense.

How did it happen?

I never use color names (except if I quick want to set a color in CSS for testing purposes) so I wonder who is using color names and why? Does all this has any real world implications?

The wonders of standards-committee bike shedding?

Nonsense. Each are in their own namespace. You can't expect something as debatable as color names to share the same values in different namespaces.