In The Sandman #21, some of the various members of the Endless families receive short biographic descriptions. Here's part of Delirium's (p 10):
For Delirium was once Delight. And although that was long ago now, even today her eyes are badly matched: one eye is a vivid emerald green, spattered with silver flecks that move; her other eye is vein blue.
Who knows what Delirium sees, through her mismatched eyes?
Is there a reason her eyes are two different colors? It appears from the above passage that it may have something to do with her development from Delight; is one color normally associated with delight, and the other with delirium?
The Wikia page says "One of her eyes is blue, and the other is green, though she can adjust them to the same color but says that hurts her," but doesn't mention why (in-universe or out) the eyes are different colors.