A rainbow in a dream typically arrives after some form of hardship, in the dream or in your waking life, and often signals hope and a sense that reconciliation is possible. Seeing one appear right after a storm can point to relief following a difficult period, a reward you feel you've honestly earned.
Heaven is the instrument of the most High God, whereby he acts upon, and governs inferior things. - Cardan Girolamo (1501-1576)