For a number of reasons (which I cannot go into here but which I have defended in my book Universals (McGill-Queen's, 2001), I am convinced that universals (properties, relations) exist and are abstract entities.
This is not a conceptualist position because I do not take "universals" merely to be entities in a mind--God's or anyone else's--that are apt to serve as general "indifferent" representations for a number of particulars. The universal redness is not in anyone's mind.
Regarding God's own essential properties, these are also universals, but God does not sustain them in existence. He simply has them. But for other universals, God has the property of necessarily sustaining them in being. So he "creates" them, not in the sense that the come into being at a time (remember, they are metaphysically abstract), but in the sense that He (necessarily) sustains them in existence.
Does this limit God? Not in any sense that matters, for all it means is that God cannot, for example, make the color red be identical to the number two. By dividing universals into those that constitute God's essence and are not sustained by God and those that do not constitute God's essence and are (necessarily) sustained by God, is my solution ad hoc? Yes, and this tends to count against my view to a small extent. But as I see it, the weight of this criticism is far outweighed by the evidence for the existence of universals in the first place.