As discussed elsewhere, NSTabView does not have a setBackgroundColor method and subclassing NSTabView and using an drawRect to control it does no longer work - as it does no
PSMTabBarControl is probably the best workaround for you. I have created several custom tab views, but cocoa does not play well with this control. PSMTabBarControl has been updated to support Xcode 4. https://github.com/ciaran/psmtabbarcontrol