Apple has released an update for the EFI firmware contained within the 2012 MacBook Air. The newest version corrects three issues that some users have been experiencing:
Courtesy of Apple
Corrects color issues when connecting to a display using HDMI.
Fixes a startup problem that could cause the MacBook Air to not boot into Windows.
Updates Thunderbolt support to fix an issue that caused the MacBook Air not to wake from sleep if a Thunderbolt device had been unplugged.
The firmware update should be available from the software update service located under the Apple menu. You can also download it directly from Apple's web site at:
MacBook Air EFI Firmware Update 2.6
Every firmware update requires running from AC power, not your Mac's internal battery. Also, be sure not to interrupt the update process by turning the Mac off or disconnecting it from power.