Underscores are shown in Edit -> Preferences -> Mail Preferences -> Colours. See screenshot. I don't *think* this is intentional but I guess it could be.
Created attachment 152554 [details] illustrative screenshot
Should be relatively simple and nice to have for F7.
I think this is not a bug. You could rename colors, so you could give them your own meaning. The underscore is used to mark an accelerator in menu, (like right click over a message and choose Label submenu), I think you need to see these underscores and an ability to change a meaning of the color is advantage as well. But I may miss something, could you write here the result, which you expect? (May be changing all predefined names without underscores, but it's against accelerators in menu)
I'd say that this is not a bug
I don't see how the underscores are supposed to be known to non-programmers. But I will not protest.
Underscores or not, it would be helpful to add some verbage to that tab explaining what those options do. It's not very intuitive. But this is upstream's problem anyway, I suppose.
Yeah, not worth carrying a fedora patch for.
It is also somewhat odd that there is an extra configuration tab for the colors and labels, but no way to add additional colors/labels. The whole thing looks very obviously extensible, unless there is some wierd interoperability constraint with exchange or something like that preventing it...
Filed upstream: http://bugzilla.gnome.org/show_bug.cgi?id=436762