hello Bendoverstewardess,
In some country like in France, Ishihara test is even more difficult because they use the 34 pages edition. If you fail, you have to ask to retake the test. There you do the lantern test and a lot of different color vision tests, the whole thing takes a half a day.
In Gatwick they use the ishihara 24 pages edition, witch you can buy at amazon book store. It makes the test much easyer. If you fail, you just have to do the lantern test.
Same happened to me by the FAA doctor, I had the impression the Ishihara was more easy.
Good luck,
og