Jack, I am puzzled by your mention of colour cast and fixing with CornerFix. I have yet to run into this problem, as has my forum partner. Both of us have used a ZM 35 on standard A7R without noticing it. Admittedly, we don't shoot the sky at infinity wide open, but still...
I also use two different adapters (Novoflex and Hawks' helicoid) without that making a difference.
So, as I said, I am puzzled.