Apple has posted MacBook Air EFI Firmware Update 2.6 for mid 2012 models.
This update fixes a color issue with HDMI displays connected to MacBook Air, resolves an issue with Windows which can prevent MacBook Air from booting properly, and also resolves an issue where unplugging a Thunderbolt device may cause the system to freeze when waking from standby. The MacBook Air EFI Firmware Update will update the EFI firmware on your computer.
You can obtain the update via the Mac App Store or the Apple Support Site (http://tinyurl.com/avtr6qz). It requires Mac OS X 10.8.2 or higher.