A reading on the Nagel Anomaloscope as a "normal trichromate" is also acceptable. The odds of achieving this if you fail the Holmes-Wright are about 0 though.
I know, as I'm very slightly red-defective, and so am stuffed.
Colour normals, blue defectives, and those with very slight green deficiences are okay, anything else is not.
Regards,
grob103