Trinity Sunday is the first Sunday after Pentecost (the 50th day after Easter) in the Western Christian liturgical calendar. Trinity Sunday celebrates the Christian doctrine of the Trinity, the three Persons of God: the Father, the Son, and the Holy Spirit. The Sundays which follow are all Trinity Sundays until the Advent season begins. This feast was celebrated as early as the 10th century. The liturgical color is white on Trinity Sunday followed by green on succeeding Sundays.
Photo of stained glass window representing the Trinity at Grace Episcopal Church, Decorah, Iowa (founded 1868). Used with permission.