I've tried knoppmyth on one Panasonic tv with an S-video in button on the remote control, and it showed up fine and in full colour with no flickering, but the two Sony's that I tried it on were all desaturated and flickery like in this pic.

I'm using an nvidia fx 5200 agp tvo, going from svideo to a scart adapter into the tv.

Anyone any idea?

IIRC (it's been a while since I looked at it) My telly doesn't support svideo input, so when I try and put svideo through a scart adaptor it looks like what you're seeing.

In the /etc/X11/xorg.conf* look for the line:
Option "TVOutFormat"

make it so it ends with: "COMPOSITE"

Option "TVOutFormat" "COMPOSITE"

* unless you're using an older version of Knoppmyth, then it's /etc/X11/XF86Config-4

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Mephi
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R5.5
Opteron 2.Ghz
1Gb Ram, 200Gb Maxtor PATA
Avermedia 771 DVB-T
Hauppauge Nova-S2 (waiting to be installed)
MS MCE2 Remote

thanks I also needed to add:
Option "TVStandard" "PAL", as I noticed it here

The only problem is, up until X loads it still suffers from the poor display (i.e. bootsplash)