Have you seen the Back to the Future film, the one in the Wild West?
Well it's a bit like the photo he has in that, when the RAF was large and had lots of aircraft, the roundel was emblazoned over the whole side of the aircraft, bright and brash... Take the spitfire as an example.... now the RAF is tiny in comparison the Roundel has shrunk in proportion to the reduction in the RAF and is fading away as in the Back to the Future photograph.... Either that or the MOD has realised they can get the paint cheaper by not adding so many colour solids into the mix.