Should an aircraft registration match the flag next to it?
That's because the aircraft (some of them at least) are leased from Aerotron Ireland Ltd., an aircraft leasing company in Drogheda Ireland.   

I only looked up one. It was EI-FVA.
Here it shows it being registered to Aerotron on Aug 23, 2016.
And here it shows it entering Blue Panorama's fleet on Dec 8, 2016.