You will find that all of the class 144s and all ten of the WYPTE 158/9s received the red and silver “circles” livery. It was only the class 155s that lingered on in the Regional Railways variant of the WYPTE red/cream livery right up until they received Northern livery.
Also, the red and silver “circles” livery was introduced by Arriva Trains Northern, not Northern Spirit: Northern Spirit tentatively dabbled in a new livery for WYPTE sponsored services when they repainted one class 158 unit, 158909, in a red and grey version of the standard “Big N” scheme, but beyond this, they were content to leave the WYPTE liveried units as they were, given that the Regional Railways revised WYPTE red/cream scheme had only been relatively recently applied. The exception to this was the class 333s, which were delivered new in the "Big N" WYPTE livery.
The class 144s had the red and silver “circles” livery applied as part of their refurbishment that saw them fitted with the same high-backed Richmond seating design fitted at an earlier date to the Northern Spirit 156s. The centre cars of the 3-car units were actually refurbished at a different time to the driving vehicles in some cases, giving rise to “pie-bald” formations in service that were part red and silver, part red and cream.
The class 141s were not quite withdrawn before the revised WYPTE red/cream livery was introduced, but you are right in saying that they never received that variant of the livery.
I love pacers and sprinters and I wasnt thinking when I put it up, I will try and redeem myself with a FNW Class and later a WYPTE class 155... 
