Entrance into Colosseum passport required?

You should always have your passport ( not a copy) kept deep on your person
It is your only form of legitimate ID and is your ticket home
IOW it’s the most important thing you carry while traveling.

So yes you should carry your passport around.

A search will bring up many threads with similar question

Hi Jon, we were on a similar tour two weeks ago and they asked to see our passports prior to entering the Colosseum. I keep my passport in my money belt when traveling so had to dig it out.

Thank you for the confirmation.
Jon