change color
change color {v. phr.}
1. To become pale.
The sight was so horrible that Mary changed color from fear.
Bill lost so much blood from the cut that he changed color.
2. To become pink or red in the face; become flushed; blush.
Mary changed color when the teacher praised her drawing.
Tom got angry at the remark and changed color.
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Source: A Dictionary of American Idioms