Early Greek and Roman iconography depicts Christ wearing a red tunic as His inner garment overlaid by a blue mantle as His outer garment. I have read contradictory accounts regarding the reasons for these colors. For example, one Orthodox author will say that the blue represents the human nature wrapped in the red mantle of divine nature. Another author writes that blue signifies the divine nature (heaven) and the red signifies the human nature (earth or blood). The latter account seems more accurate to me; however, I’d gladly yield to an art historian on this matter.
Unlike depictions of our Lord and Savior Jesus Christ, the depictions of the Mother of God are not as consistent. Eastern icons nearly always have the Mother of God in a blue dress and with a red mantle. This is the case in Greek icons in which she holds the Christ Child, her station at the Crucifixion, and even on her bed at the Dormition.
However, there are exceptions so that Mary wears red and has a blue mantle. This latter arrangement is more popular in Western depictions. For example, Raphael always pained Mary with a red dress with a blue mantle whether she be depicted in her espousals or in holding the Christ Child. Catholic depictions of Mary Assumed always have her wearing a blue mantle.
Notably, Our Lady of Guadalupe is wearing a red dress with a greenish/blue outer mantle.