I agree that the for the price they paid for the cameras there shouldn't be a problem - purple fringing could be coming from the lense used, though.
As for the composite argument - agreed, but I would ask if all of the elements in the shot examples were CGI, or if some of it was either the Mt. Etna footage or miniature, which they used throughout the Mustafar sequence.
I'm thinking monitor calibration could be the culprit now, however.