Red-letter day: a day remembered as especially happy and
significant
Red letter day is any day that is of specific significance
according to the medieval church calendar. They used red ink to
show these days. Red letter day is a synonym for a public holiday
in many countries of the world.
Red letter day would be any day that you feel is special to you
or holds something significant to you that is of importance to you.
Red letter day should be a happy ocassion to you.