Commentary for the film’s DVD edition chronicles the historical research done by [Director Cecil B.] DeMille and associates…
The man who designed Moses’ distinctive rust-white-and-black-striped robe used those colors because they looked impressive, and only later discovered that these are the actual colors of the Tribe of Levi.
Wikipedia (2014). The Ten Commandments (1956 film). Available http://en.wikipedia.org/wiki/The_Ten_Commandments_(1956_film). Last accessed 27th Sep 2014.