Hi Richard,
I found that the issue has to do with a Mac playing back the Avid HD codec QTs, but importing the QTs into Avid is fine. So even though the quicktime movies continue to have color bands when played in Quicktime on the Mac, they look fine when imported into the Avid using Avid DNxHD 220 codec. I have no idea why this happens but at least the final result in Avid looks ok.