This lovely dress, which is fashioned after paintings found in the tomb
of Nephertari, is one of the graphics that were never used in the game.
To activate it, you will need a savegame editor like DaggeD.
The best item to use is a formal eodoric. Select it and simply increase the number of the image by one, from 162 to 163. That's it. Save and load the game. You will find the dress, that is especially fetching on Redguard ladies, in your inventory (or ship, or house, wherever the eodoric was).
And in case you're wondering: yes, it is a very authentic representation
of Egyptian court fashion 3000 years ago. Dresses like these were
popular for centuries. Usually they were made out of sheer, plaited
fabric, but the paintings of queens and godesses show a texture that
may well represent metal plates. Compare to the left Queen Nephertari
and the goddess Isis. I'm not quite sure which is which, but I think
it's the goddess who models the dress we are talking about.
Image 164, by the way, is a bowdlerized and thus far less authentic version with additional boob caps such as the eodoric has.