I'm pretty sure the aeromedical guide explicitly states the conditions for all tests (including what light you need to shine on the PIP), so I doubt they'll let you wear (unapproved) contacts or glasses to correct color vision. That being said, I HATE the ishihara test, and have failed it before, but usually pass. I am slightly deficient, but can usually make it out if given a few courtesy seconds to see it. Worst case, they can do the FALANT as a backup (although I hear this may not be approved anymore?) and if you can't pass the FALANT, you are seriously deficient/colorblind.
If you want to game it... you can always buy the various PIPs on amazon.com... just saying. But if you can't see the plates EVER, it won't help. It may only help you "see" the weirdly cursive numbers and/or know which plates are trick plates that show you nothing.
Not condoning gaming the test, just saying it's out there.