We had a similar problem with a young rooster years ago, his comb would turn bluish even in rather warm weather. He had been treated with ivermectin internally , for mites as precaution in case he had mites near ears. Vet felt the slight lack of circulation may be irritating to him , he had slight heart problem ,and social trauma from competing with 2 other roosters , once he was seperated into his own pad with his own girls he stopped it. but it may have been the ivermectine. to this day we really dont know . He did have a slight heart problem so didnt live a very long time , If I remember right it was around 7 yrs.but had a happy life. could be caused by many things . sometimes its social irritation, usually there is some form of external irritation