People don't notice the the figure of Mary in the "Pieta" by Michelangelo is larger than life with a corresponding larger than natural mass,
or the figure of Jesus is smaller than life with a corresponding smaller than natural mass. Is that due to color and light?
There are several possible explanations for the relative sizes of the figures of Mary and of Jesus in the "Pieta." Michelangelo had specific reasons for carving the sculpture as he did; the effect is not due to light or color on the stone.
The process of depicting a full-grown man in the lap of a woman is a challenging one. Michelangelo may have been forced to adjust the proportions of the characters in order to create the overall effect he wanted to present. Mary's robes contribute to the apparent mass of her figure.
Michelangelo portrays Mary as being young, which could reflect his wish to show that the passage of time did not impact the mother of Jesus; another theory is that the sculpture is meant to represent Mary holding the baby Jesus with foreshadowing of what was in the future for that baby.
The smallness of Jesus's body may also be a way to convey the brokeness and loss of power after His death.