I flew for 35 years and have not had any more colds or other illnesses than anyone else.
The only colds I got are from the person I am married to whom is in the medical profession who frequently has colds.
I know some crew get annoyed when other crew come to work with a bad cold as they are afraid of catching the virus and having to go sick themselves. I have never caught any colds or viruses from another crew members or passengers as far as I can remember.