The term 'turn crimson' can be solved by two crossword solutions: 'BLUSH' (5 letters) and 'REDDEN' (6 letters). Blushing is a physiological response to embarrassment or other strong emotions, and is characterized by an increase in blood flow to the face, resulting in a reddening of the skin. Reddening is a similar phenomenon, but can also refer to a reddening of the skin due to sunburn or other external factors. Both terms describe a change in skin color from its normal hue to a reddish hue.