All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Using a dye to cover grey and white hair does not affect fasting since it does not involve eating, drinking, or anything to their effect. This is the predominant opinion.
Allaah Knows best.