Been down this road myself in the UK. Failed Ishihara, and Holmes Wright, in both office lights, and in the dark. (Confuse white and green). Failed at CAA first time, then went to the colour vision clinic at City University and failed again.
While at City I did the Nagel Anomoloscope too. JAA stipulates you must be able to pass as a "normal trichromate".
The Nagel Anomoloscope consists of looking into an instrument at a coloured disk, split in two halves. The idea is to match the colours on each half exactly, by adjusting two knobs: one for red-green colour, and one for brightness.
Using the Anomoloscope, I was diagnosed as a protanomolous trichromate - ie red deficient.
Thus, I confuse white with green on the Holmes Wright, as the white light is apparently: "quite greenish, to help those who are green defective (deutanomolous trichromates) to see it as white".
8% of men are green deficient, 2% red deficient, and <1% blue deficient.
The great advantage of the City tests (including the anomoloscope) is that they can quantify any defect you might have.
Apparently, I'd be okay if I was similarly defective in green, but as I'm not, I'd best get on with my 2nd choice career.
cheers,
grob103