Enya's visual inspiration, for the most part, comes from Maxfield Parrish, an American artist from the early 20th Century. Below are some paintings of his which have obviously directly inspired her.
Further below that, you can find a painting by a different artist that seems to co-inspired the music video for "On My Way Home"

Some of the paintings that inspired the music video for "Caribbean Blue"

A Departure: Man in Moon

Mutabile Semper, Chocolate

Garden of Allah

The painting that inspired the cover for The Memory of Trees

The Young King of the Black Isles

And the two painting s that inspired the music video for "On My Way Home"

The Lanternbearers

A short biography on Enya
A short biography on Maxfield Parrish