I've been trying to duplicate the results your brother is getting, with my D800. I have the same lens, shooting raw, Auto WB and H2.0 ISO. My lighting is a 4 bulb chandelier where I can control the tungsten lighting intensity. My shutter speed/aperture is the same as your photo. I don't have LR so I use CS6. I can't get the purple corners your photo shows. It appears that any dark area in your photo shows purple and that includes the lens vignetting darkening in the upper corners. My photo has the same corner darkening but there is no hint of purple. I have no idea where the problem is with your brother's D800. How are the blacks at the lower ISO settings like 1600?