Going through customs flying from Paris to Italy
 

We will be flying from the US to Paris on Air France. Five days later, we will fly to Rome (FCO) on Air France. Will we need to go through customs when we reach Rome?

No.

There is no immigration. After you claim luggage, unless you have something to declare or get stopped for inspection, you just walk out the green doors.

I can't remember specifically at FCO; but I think if you don't have checked luggage, you should be able to bypass luggage claim and just walk out.

Customs and immigration are two different things. If you have something to declare, you go through Customs. If not, you don't have to go through anything because you're within the EU.

Thanks for your help. Please explain what you mean "if you have something to declare." We will probably have a few items - no liquor or perfume - that we will have purchased in France. Do we need to declare those when we enter Italy?

No.
Only when your goods are beyond what is considered to be for "personal use". To give you an idea of what kind of allowances we are talking about: beer/wine 90 liters, hard liquor 10 liters, 800 cigarettes, and so on. If you carry more you may have to pay duties.
Whatever personal shopping you have in mind for Paris (a few new clothes, souvenirs) is not what these limits are about.

Intra-EU passengers "clear customs" (which is not a person-by-person check, but random spot controls) by choosing the blue exit after bagagge claim. If no blue channel is available, chose the green exit -- assuming that you will not be traveling with more than 10 liters of Cointreau per person :-)

ahh! Now I get it! Thanks so much.