If you look at the pictures of the aircraft when it was operating for skyservice it was never actually painted in their livery. It was the First Choice livery with Skyservice stickers. It was therefore probably easier to put First Choice titles back on the plane rather than re-paint it in the Thomson livery!
JetPhotos.Net Photo » C-GTDH (CN: 1605) Skyservice Airlines Airbus A320-214 by Keith Wignall