I'm normally reluctant to advise people to powerwash decks, but it's the best way with ipe.
Power wash with a machine capable of 2500-3000 psi pressure. If the deck is severely weathered, a deck wood stripper can be used when power washing. This should remove most of the gray and expose the original wood coloration.
To maintain the 'new wood' appearance use Penofin. It's a penetrating oil finish with a high UV inhibitor rating.