Unfortunately, Charlie was put down sometime ago now. He did have tumours. I convinced my vet to try to remove one and he wasn't able to get it all. So, it was inevitable it would return. He got 6 more months of reasonable quality of life, but the day he couldn't fly anymore, I had him put down and necropsy showed that he had a completely inoperable cancer at this point.
It is possible that his cere started to go blue again with some of the treatments he had along the way, I don't quite remember.