Wow Glom,
I feel sorry for you buddy! You've clearly been through the mil on this one, and you've probably just sounded out what a lot of us 'colour defective' types have been thinking for years. I've got two bits of good news for you, however.
First, you'll find no subversions at Gatwick - quite the opposite. True they held me back on colour for several years, but my borderline condition has finally been recognised by CAA Medical thanks to its introduction of the Beyne's Lantern test.
And that's the second piece of good news. The Beyne's test is roundly considered to be the easiest colour vision test to pass. I've described it at length earlier in this thread. It sounds like 'red-green' is your problem area, and while the Beyne's test will examine this common condition it leaves out brown, which cab be a tricky mix of red and green.
My sense is that CAA and the rest of the medical community is coming around to a better understanding of colour perception and its affect on flight safety. You only have to pass one of the three tests at Gatwick - Ishihara, Holmes-Wright, and Beyne's - to be passed fit as colour safe, as I belatedly was. So, go to Gatwick with an open mind. You might pass on Beyne's too. If not, at least you will know your colour vision probably is too defective for today's standards. Beyne's is truly the easiest test...at least my eyes thought so.
Good luck
Dan