You're welcome - that's what we're all here for. :O)
There have been many changes in ticketing this past year; some happening long after the latest RS guide went to press. It's always best to go to the official websites for the attractions you wish to see as hours and entry fees and all sorts of stuff can change on a dime. Don't know what those are? Just ask, as you've done here.
As well, you can check the guidebook updates section of this website for changes other travelers have reported since guidebooks went to press. Here are those for Italy, and note that the change in ticketing for the Colosseum is included (under the Rome heading) and with a live link to the current ticketing resource:
https://www.ricksteves.com/europe/italy/guidebook-updates