My M7 also has the purple problem. I've searched everywhere for the true fix, but the only one that people have had success with is to send it back for repair and it's not clear what the repair is, although it appears to be the image sensor.
I can't see that it is software as, surely, HTC would have rolled out an update, rather than have the expense of handling 100's of returns.
My phone is without warranty, so being an engineer, I bought a sensor on ebay and swapped it out, however, the purple problem is still there, if not worse. The sensor I bought was a cheap one from hong-kong, so could well be a copy or the same model/type etc. as the original.
A thread on reddit asks for folks to upload their sensor info to see if there is a trend, but I think it's inconclusive; some have the problem, some don't.
There's a video on youtube of a guy using his finger as a heat sink on the back of the image sensor to reduce the purple tint; I've tried this and it does not work on mine with this 'new' sensor (I didn't try this with the original sensor).
Another thread, that I cant find now, said, after getting HTC to fix it, the sensor make was different. My sensor is now:
st vd6869(1.0) cinesensor 0000-00-00
The zeros on the end is supposed to be a date, but after swapping it out, it now has zeros. There was a date before but I didn't make a note of it; the rest was the same.
So, my next step is to find the image sensor that fixes the problem, then I can buy one and swap it out.
Have any of you come across it or know any more info that might lead me to it?
Many thanks!
Mike