A1200 Brown Screen tint issue again, but...

[16vMonkey]

So yes I've got the dreaded brown tint issue, and reading online there are a number of articles and videos about using ProTracker to highlight what colour channels are missing or low, by changing the colour bars. 

For example: https://www.youtube.com/watch?v=D8LGfxu2zpI

But when I drag the sliders I appear to get full range of RGB, but anything grey has a brown tint, including the Kickstart boot screen, its not purple, its brown.

Any clues as to what to check?!