Actually, you can use an app for that. :) I threw a copy of myLite Flashlite onto my ipad. It filled the screen,

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Actually, you can use an app for that. :) I threw a copy of myLite Flashlite onto my ipad. It filled the screen, and one of the options is a slider to choose what color the screen is, so I went through the red, green, and blue that way.