A full repaint won't be required, unless some fool has allowed the "green aircraft" to be painted in a charter air line's colour scheme (aren't all Voyagers being delivered in a proper military paint scheme?).
According to the Flight article, that's exactly what some fool has done:
Unlike the eight Voyager tanker/transports already in use with the RAF’s 10 and 101 squadrons and AirTanker’s G-VYGG, the new aircraft will be painted white and receive Thomas Cook livery
There's an artist's impression of the livery in the article.