Two users have reported on this.
See:
http://en.wikipedia.org/w/index.php?title=User:AussieLegend/Vandals_etc&diff=prev&oldid=560719781
And:
http://en.wikipedia.org/wiki/Wikipedia:VisualEditor/Feedback#Font_colors_in_signatures_changed
I realize that this is probably tied into other behavior, but I lack code-fu to determine what. :)
Maggie
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=42803