The intention was to have all the a/c in the buzz yellow and purple scheme. However with the takeover by Ryanair, the intention is to rebrand all of them in Ryanair colours. At least one (G-BZZG) is still in unbranded CO colours. G-BZZJ that has just the yellow body colour and no logo's was, at a guess, probably halfway through being painted when the decision came to leave them as is.