Red - the color of Christ's blood, which atones for the sins of humanity, the color of Christ's Resurrection. Priests start the Easter service in white garments, then change into red ones and serve in them for all forty days of the Easter services.
White - the color of detachment from the world, the color of prophets, saints, and angels. In white garments, priests perform memorial services and during the great feasts of the Lord.
Yellow (gold) symbolizes divine radiance and the Son of God. It is also the color of the halos on icons, the garments of priests during Sunday services, and most festive services.
Black - the color of death, hell, the color of ignorance - the whole world was dark until God created light. But it is also the color of monasticism - a monk "dies" to the worldly life when they turn to God. Not only Orthodox but also Catholic and Protestant priests wear black robes.
Green - the symbol of eternal life and the Holy Spirit. Green domes on a church mean that it is dedicated to the Holy Trinity or a saint.
Blue - the color of heaven. Christ and saints are often depicted in icons wearing blue and dark blue clothes, as they dwell in the heavens. The combination of white and blue is the color of the Mother of God.