What is a black tie event?
White bow ties are worn with morning coats of varying colors. Evening wear requires a black coat and black tie. A man's evening wear is meant to keep him from clashing with his partner's gown, so black and white are preferred.
Absolutely, as long as the event is not a wedding. When an invitation reads "black tie" it means the event is formal. A lady may wear any color she chooses to such events. The exception to this rule is a wedding. Many people consider it inappropriate for a lady other than the bride to wear white. You don't want to compete with the bride!