Wyse T50 RDP Colors Problem

Hye,

I'm a new user for the Wyse T50 and I would like to configure an RDP session for testing this thinclient.
In the RDP connection, we can choose the Window Colors (15,16, 24, 32 bits).
I've tested all this choice but when i'm logging to the TSE 2003 Server R2, the session is always on 256 colors ?

Someone could help me ?

Thnax