Moonstone, by the name, is believed to have connections to the moon and to the subconscious and unconscious. It is believed to promote emotional openness to new experiences. This openness is part of how moonstone is thought to relieve stress--by calming the mind and soothing the spirit.
Peach: associated to the sacral for reproductive health
White: associated to the crown chakra for spiritual or psychic experiences
Grey: associated to the heart for emotional changes.