The answer
Some churches have a single dome representing our Lord Jesus Christ, the Head of the Church who is enthroned in heaven. Thus, inside the dome we mostly find an icon of Our Lord, or it is painted in a heavenly blue color and decorated with icons for angels and/or stars. Other churches have three domes representing the Holy Trinity, others have five domes with the main one in the center representing our Lord surrounded by four smaller domes representing the four evangelists.
Fr. Tadros Yacoub Malaty