Thanks Bruno.
In theory this shouldn't happen at all since I even have the upgrade that was suppose to fix this in xStream.

Since I posted here I've done some reading about this in other places, and it seems to be connected with the use of a color mixing function in mixed materials....which was what the upgrade I have was for, among other things.
And there's a lot of mixed materials with color mixing functions in this render, so I think that's the reason.

C.

"Keep smiling, it makes people wonder what you're up to."