Well it looks as if these 4 aircraft will be sole use of Air Lingus Regional hence the reason they will be painted in the Air Lingus Regional livery.
All other aircraft will remain in Aer Arann Livery as they will be used on their PSO's and anyth other route that will remain Aer Arann.
It would make sence that Aer Arann plans to update their livery on all their remaining aircraft to bring them into one livery but i can't see this being done until W10 as the aircraft is very much needed especially with the 4 operating Aer Lingus Regional.