I went into the local Ian Allen bookshop (yes, there is one in B'ham), anyway, months ago I rmember browsing and flitting through books, and I noticed many A/C & their various highly coloured paint & markings for the Formation Aircaft. Those A/C were typicaly older/more worn-out A/C that were used during the bomber stream formation, before the bombers flew off to their destinations.
Normally a few repainted bombers as lead and box formation lead A/C's, with some highly painted fighters/escorts for shepherding forming bombers into their assigned 'Boxes'. Think of it like visual, airborne airtraffic control, they, the Formation Keepers & Shepherds, landed once the bombers streams were at height & in formation; sometimes they assisted in aerial escorting duties into the British parts of the Channel and North Sea.