She was raised on Long Island and began her acting career in the soap opera The Edge of Night, playing an heiress and former terrorist. In seven months on that show her character survived seven murder attempts and ended up marrying her stepbrother. She followed that role with a longer stint on As The World Turns, originating the role of Margo Montgomery, a character which is still part of that show over 20 years later.

She has appeared on a number of prime-time television shows, starting with Foley Square and several early episodes of Chicago Hope. She played Lisa Wiseman on the 1999 series Now and Again with Eric Close and Dennis Haysbert.

Colin has also been in a number of movies, the most well-known of which are probably Something Wild (1986), Three Men and a Baby (1987), Independence Day (1996), Unfaithful (2002) and First Daughter (2004). Also, she appeared in the play Jackie: An American Life, in which she played Jacqueline Kennedy.

Colin is a pro-life activist and is the honorary co-chair of Feminists for Life, a nonsectarian, nonpartisan organization opposed to domestic violence, child abuse, infanticide, and abortion.

She is married to actor Justin Deas, and the mother of two sons. The two met when they were on As The World Turns when he played her love interest, Tom Hughes.