Same Problem with WinFast2
I had the same problem with a WinFast2. When reading the documentation of (latest) NvTV version I found a hint that perhaps the msc value has to be adapted when BT686/689 Brooktree chips are used.
I was able to fix this problem by selecting NvTV page "BT Regs2" and tuning msc register values. In my version "msc" it is the last entry in the first row of values.
With my card a value of 6455 for first msc register brought me color which is only 1 above default value (6454). Don't forget to click Apply after every change or use AutoApply.
I hope this helps.
This is the text I found in documentation to NvTV 0.4.4:
On some systems, especially with Chrontel encoders, the frequency of
the color carrier is wrong. You can change this frequency with the
two 'fsci' spinbuttons on the Chrontel register page, and similarly
with the 'msc' spinbuttons on the Brooktree register page. Don't
forget to 'Apply' or 'AutoApply' your changes. If you need to change
this value and find ones that work for you, please mail me the mode
and the values. There is also a 'pseudo' TV system called 'PAL-X'
which has a few modes with different color carrier. Maybe those work
for you, maybe they don't.