https://www.faa.gov/about/office_org...ch/item52/amd/
Download the above. Take it to any optometrist and tell them you want to be tested. If you fail one test, keep trying other tests until you find one you can RELIABLY pass.
If you can’t pass ANY of them, it will get uglier and more expensive. But buck up. Over 10% of males have some degree of color blindness. A large majority of those can pass at least one of the standard tests.
As far as the Ishihara this is the standard:
Ishihara pseudoisochromatic plates: Concise 14-plate edition: six or more errors on plates 1-11; the 24-plate edition: seven or more errors on plates 1-15; the 38-plate edition: nine or more errors on plates 1-21.
That is to say, you are DISQUALIFIED if you miss the indicated number or greater.