(as) red as a ruby

Extremely flushed and red, especially in the face, as from embarrassment, anger, or physical strain. My father was as red as a ruby by the time we reached the top of the hill. I was afraid he might have a heart attack or something! Oh, Mike definitely likes you—he turns red as a ruby every time you're around! Mom's face went red as a ruby when I confessed that I was trying to sneak out of the house to go to a party.