How to get my ChangeGamma routine be called

[Juergen Beisert]

Hi all,

I'm writing a xorg driver for my cpu/graphic. I register a ChangeGamma 
function in the pScrn structure and add the line "Gamma 1.2 1.2 1.2" to my 
xorg.conf.

The Xorg.log states a 
[...]
(**) MYDRV(0): Using gamma correction (1.2, 1.2, 1.2)
[...]

But nothing else. My ChangeGamma function will never called. Whats going 
wrong?

Regards,
Juergen