Chrominance problem with my C64 S-Video out

I recently purchased a S-video to VGA adapter for my C64. But, big disappointment, the frames eke out a miserable dull and grey existence. What’s wrong here? And is the blame to be attributed to the C64 S-video out, or to the adapter? In contrast to my vintage 1987 Commodore, warranty for the latter hasn’t run out yet ;-)

So, let’s take out the scope for some trouble-shooting attempts.
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