DISPLAY SHOWS RED GREEN BLUE GRAY
In MacBook Air, when the unit switched-ON, the entire screen starts alternating colors of red, blue, green, gray, gray stripes, etc.
But video in the external display is OK.
Is it the display or logic board problem?
Try Reset PRAM.
Some of the display settings are stored in PRAM.
Reset PRAM: http://support.apple.com/kb/PH14222
If this does not help, you may have to take it to the Apple store to have it checked out.
Genius Bar reservation
http://www.apple.com/retail/geniusbar/
Best.