Blushing
Blushing was a physiological response that would cause the face to redden, typically due to embarrassment or shame.
In 2365, Geordi La Forge explained how he'd deduced that the Mariposa colony clones lied about William T. Riker and Katherine Pulaski's whereabouts: "Commander, with this I can see better than your average person. Now when someone lies there are certain physical manifestations. Variations in blush response, pupil dilation, pulse, breath rate. Doesn't always work with aliens, but humans? Got'em nailed." (TNG: "Up The Long Ladder")