No RealNC is right. Fglrx uses ranges like 16-235 to represent RGB colors when doing colorspace conversion for Xv instead of 0-255. If you have gstreamer-tools installed, you can easily test this.
This should give you a white picture, as radeon ddx does, but fglrx gives you a grey picture.
gst-launch-0.10 videotestsrc pattern=white ! xvimagesink