Paul Joy and John Ford brought this to my attention today. I had not noticed it before, but now I’m looking for it, I can see it and re-create it quite easily. Not sure exactly what it is at this stage, but if you overexpose the image you can get a solid green or purple block of colour. I did see this over a large area of one image, but more normally you see it on specular highlights or high contrast edges. It appears to be a mixture of flare and blooming or sensor overload. It’s not pretty and very distracting when you have an image full of green or purple flecks. Green is the predominant colour. It may be related to the operation of the cameras knee circuit or it might be a optical issue (which would be hard to fix). I’m on a shoot tomorrow, but will look into this worrying artefact on Wednesday.