I don't think it's possible to memorize the ishihara book of numbers, there many different versions. But there is a doctor in Maryland who guarantees 100% that you can pass the test with his color correction system. Check out his website http:/www.colormax.org . Color vision correction changed my life as I know have my dream job. I personally thinks its discrimination against color blind people. People who wear contacts lenses can't pass a regular eye test without their lenses. So I why should be any different for color blindness!