Difficult Sentence!

It's not very poetic, but this is a fair equivalent in 21st-century English:

Spirit of Beauty, you who consecrate everything in human form or of human mind that you shine upon - where have you gone?

Here is what it means
Shelley speaks of the quality of beauty as though it were an invisible being that blesses people and ideas, elevating them above the ordinary and everyday. The fact that the spirit of beauty uses its own hues indicates that the ways in which it makes things beautiful are unique, special, and varied. But the question is asked "Where have you gone?", indicating that beauty found in people and ideas is increasingly rare. If it was true in Shelley's day, it's even more true now.

But if it's translation you want, syntinen has it pretty much sewed up. I would add:

Spirit of Beauty, you who, with your own colors, consecrate everything in human form or of human mind that you shine upon - where have you gone?