identify this movie - A guy and a girl become colorful in a black and white world

You are thinking of Pleasantville from 1998.

From IMDb:

A brother and sister from the 1990s are sucked into their television set and suddenly find themselves trapped in a 1950s style television show. Here they have loving parents, old fashioned values, and an overwhelming amount of innocence and naivete. Not sure how to get home, they integrate themselves into this "backwards" society and slowly bring some color to this black and white world. But as innocence fades, the two teens begin to wonder if their 90s outlook is really to be preferred.

An awesome film, I might add.