The first Jet2 A321NEO is undergoing ground testing at Hamburg under test registration D-AVYK (Jet2.com registration will be G-SUNB) - delivery date is not yet confirmed, and no sectors have been scheduled thus far up until mid-June, so it might be a while before it enters revenue service.
It's planned for Holidays livery, and I imagine all of the new aircraft will have this due to Jet2's focus on the package holiday sector - I imagine eventually we'll see fewer .com liveries in the fleet as aircraft are repainted, retired, or returned. The airline already has a majority of Holidays capacity with flight-only bookings taking a smaller percentage of seats.