For some reason the mixer applet isn't using Bluecurve icons anymore. I found this researching bug 106138.
*** Bug 133348 has been marked as a duplicate of this bug. ***
Should be fixed in rawhide now: * Thu Oct 7 2004 Mark McLoughlin <markmc> - 2.8.0-4 - Fix mixer icons bugs - #134224 and #134773 (It was using stock-icon based theming, but you've removed that sutff now)
markmc : This problem doesn't disappear completely. When mouse wheel button scrolls up/down on mixier applet, mixier applet icon changes to no bluecurve on middle state. * gnome-applets-2.8.0-5
Pretty sure Alex fixed this earlier today in redhat-artwork
Already fixed in latest redhat-artwork.