Got me stumped too – never saw any plain yellow bars at Brawdy during the cammo era, and the only photos I can find of XX327 don’t help either, apart from clarifying that it is a Boscombe jet….

Edit: just been having a think after seeing comment about possible unfinished paintwork….. 234 Sqn markings had a different shade of yellow edge to them, could possibly have been applied as a block prior to back/red diamonds applied on top?

234 Sqn Hawk