Apple today released Apple TV Software Update 4.2.1 which features:
• TV compatibility: Addresses issues that may cause the screen to flicker or display incorrect color on some older TVs.
• Wake from sleep: Addresses an issue where Apple TV may not wake up from sleep.
• Audio: Addresses an issue where audio may not be heard on some TV models after switching from another input.
• Stability and performance: Apple TV Software Update 4.2.1 includes stability and performance fixes for Apple TV.
Apple TV Software Update 4.2.1 is for 2nd generation Apple TV units and is available Settings>General via your Apple TV.