I initially wrote:
Well, Homer did say he was blond …
Homer in Hymn 7 describes him as follows:
Dionysos appeared on a jutting headland by the shore of the fruitless sea, seeming like a stripling in the first flush of manhood: his rich, dark hair was waving about him, and on his strong shoulders he wore a purple robe.
It’s Hesiod who said:
And golden-haired (chrysokomes) Dionysos made blonde-haired Ariadne, the daughter of Minos, his buxom wife: and the son of Kronos made her deathless and unageing for him. (Theogony 947ff)