A lot would depend on your exact form of colorblindness. The first step would to have (outside of an actual medical application), have a good AME (Dr. Bruce Chien in Peoria, IL is one of the ones who has a lot of experience with this). He uses several different sets of plates that are acceptable to the FAA and tests the vision in what he calls his "thermonuclear chamber" which is really the vestibule to his office that is completely flooded with natural sunlight which makes the plates easier than the average office fluorescent lighting. If you can't pass the plates he has a few acceptable alternate tests you might pass.

I'm pretty sure, this is one of the cases where all is not lost if you take the test. You won't be denied a medical if you are colorblind, it will just be restricted to day and no light gun signals. It wouldn't bar sport pilot. The last ditch is the FAA SODA test where they shoot light gun signals at you from the control tower and see if you can correctly identify them (most tower controllers during slack times will be glad to send you some signals for practice). They also will ask you color questions about things on a sectional, but there are enough other clues that you can answer those even if you had totally monochromatic vision.