We just released Craft CMS 2.6.2916, which introduces a slew of accessibility improvements for the Control Panel, especially around Garnish UI elements like menus and lightswitches.
(What is Garnish? It’s a UI toolkit that powers much of the Craft Control Panel interface. Oh, and it’s under an MIT license now, so feel free to help contribute!)
Our goal is to make the Craft Control Panel completely WCAG 2.0-compliant. We’ve still got a long ways to go, but this is a strong first step. If you or your clients have any specific accessibility needs not currently accommodated by Craft, please let us know.