I have three accessibility items.
First, I'd like to drop the HighContrastInverse & LowContrast themes. GNOME dropped support for these two themes late this cycle and they can no longer be set in an unpatched gnome-control-center. The idea is that this one theme will be significantly better than trying to support three mediocre themes. I hacked in support for these themes for 3.6.0 in Ubuntu 12.10 but gnome-themes-standard 3.6.1 isn't building for me yet with the hack.
The two dropped themes aren't really terribly usable anyway, and unless someone steps up to maintain them, it's not worth the headache to try to keep them building.
My second item is a requested feature. It would be really great if Unity would support the zoom and color effects built in to GNOME 3.6. By setting inverse or adjusting the brightness/contrast this way, all apps (even web pages in your web browser) will respect your color setting.
http://bicha.net/img/gnome-zoom1.png http://bicha.net/img/gnome-zoom2.png http://bicha.net/img/gnome-zoom3.png
And finally, Unity includes a mostly hidden accessibility status menu. It's probably a good thing it's hidden as it's almost useless at the moment. I filed bug http://pad.lv/1067166 requesting that a replacement be designed and included in 13.04.