Beauty is in the Eye of the Beholder -

Beauty is in the eye of the beholder - Margaret Wolfe Hungerford- 1878

Shakespeare expressed a similar sentiment in Love's Labours Lost, 1588:

Good Lord Boyet, my beauty, though but mean,
Needs not the painted flourish of your praise:
Beauty is bought by judgement of the eye,
Not utter'd by base sale of chapmen's tongues

Benjamin Franklin, in Poor Richard's Almanack, 1741, wrote:

Beauty, like supreme dominion
Is but supported by opinion

David Hume's Essays, Moral and Political, 1742, include:

"Beauty in things exists merely in the mind which contemplates them."