Comment 23 for bug 312993

Alexandre: You're not getting enough sleep :-p
The Tango icons colors is just a modification of the tango set (wich was intended to be the most close possible to the art libre set). It was made to provide more familiarity. One of the main critics to the Tango set was that the toolbox icons became too different than the default set, and people would not recognize them (which sounds a little bit silly to me, but a lot of people seemed to agree).
The Tango icon set was complete, but several people rejected it because it was too different than the default, so we created an alternative version with colors and shapes closer to the default set, but with a "tangoified" look.
That's Tango Icons Colors.
Both on IRC and mailing list, a lot of people who initially didn't want the Tango set seemed to like that modified set, and said that they wouldn't have problems to use it.

manzur: The set is complete, yes. But there isn't consensus about if it's prettier or not. I like it, you like it, but several people seems to prefer the original.
But the original is broken. It has style errors, alignment errors, jagged borders and a completely nonsensical color palette. In my opinion it has to be fixed to be "the default".
Somebody (I can't remember his name) created the refreshed version I attached here). It has the same look and feel but the majority of issues of the original set have been addressed.
If we won't get Tango icons as default (the discussion was long and everybody has valid points) at least make this corrected set the default. That's my proposal.

Luca: AFAIK the works on the hicolor theme have broken the themeability. I think the changes should be rolled back to the previous state and move the hicolor stuff to branch until it's ready.