When I used to use my A1200 on a TV set I used the RF modulator. The
strange thing is, my TV can't take NTSC (only 60Hz PAL) so when using
the NTSC monitor drivers AmigaOS doesn't seem to be using the NTSC
broadcast colour mode on European machines, just 60Hz PAL.
There is no monitor driver in Workbench for 60Hz PAL strangely enough.
What you appear to have happening is a PAL Amiga on an NTSC TV... or
an NTSC Amiga on a PAL TV.
The only way to avoid this is not by using the RF or composite outputs
but using the Video output pins. This will bypass colour encoding
PAL/NTSC) and give you crisp, region free RGB.
Strange and complicated I know.
:-)