The phrase 'painting the town red' is an idiom that means to go out and have a wild, exuberant night of fun. To find antonyms for this phrase, you would have to look for words that suggest a lack of activity or excitement rather than wildness. Words such as 'calm', 'quiet', 'boring', 'dull' and 'sedate' are all antonyms for this phrase. If you want to convey the opposite of painting the town red, you might say they were "mellowing out at home" or "having a quiet night in." Instead of painting the town red, some prefer to "keep a low profile" or "stay out of trouble.