I don't have your device, but let me guess.
Your phone should be on WM5 and it seems that your phone is in skin mode.
There are.. 3 ways to solve it
(1) Try the default dialer
(2) Use a customized dialer
(3) Edit the skin
- Details -
(1) Disable the Orange skin, by editing the registry, go to
modify the Enable from "1" to "0"
(2) Go to this thread
Grab one of the colour that you like and install (can be uninstalled if you don't like it)
(3) There is a file in your windows directory that is used for the skin background (open one by one on your PPC, or better, copy everything from your PPC to your PC), copy that into your PC, modify it, and paste it back.
NOTE: All of the methods stated above require restarting the device.