UKARA is just a way of proving your defence and is not needed, it just makes things easier. The defence is the of " Acting out Law Enforcement or Military Scenarios". You are not doing this, so the airsoft defence does not technically apply to you. After all in the firearms world lots of three gun and other paractical shooting disciplines use wildlly coloured guns to get away from the image of them being weapons. I agree this is a bit of a pisser but it is fact.
If you want a black airsoft gun I suggest you play your three games in not less than two months and get a site membership, wether it is linke dto UKARA or not, that is your proof of defence. Who knows you may actually like it. Otherwise nice blue or red slide ona Hi Capa or Glock it is.