Here are a few frame captures from Ringer Spy Bellerophon of the Nazgûl Steed maquette from the latest “Creatures of The Two Towers” video on
These have been brightened and enlarged for your viewing pleasure, although the framing of the maquette in the original footage makes the images somewhat cryptic to say the least. It’s quite possible that the intercut images of the John Howe Nazgûl Steed in the same video gives more of an accurate idea as to how the fell beasts will appear in TTT and RoTK.

Nazgûl Steed #1 Nazgûl Steed #2
Nazgûl Steed #3