Here's a partial text. Note: recreational pilots get a third-class medical. Commercial pilots need first-class.
E. Defective Color Vision. When the applicant has a
defect in color vision, the inspector must ensure that the
applicant demonstrates the following abilities:
(1) All applicants must demonstrate the ability to
read aeronautical charts for print that appears in various
sizes, colors, and typefaces; for conventional markings in
several colors; and for discrimination of terrain colors at a
distance of 16 inches for both day and night conditions.
(2) All applicants must demonstrate the ability to
read aviation instruments, particularly those with colored
limitation marks and colored instrument panel lights,
especially marker beacon lights and warning lights.
(3) All applicants must demonstrate the ability to
recognize terrain and obstructions. etc etc
(4) For first-class medical certificates, applicants
with defective color vision must be tested at twilight
or at night. The test for a first-class medical
certificate is much more comprehensive than the tests for
second- and third-class medical certificates. In addition
to the above exercises, the applicants for a first-class
medical certificate must demonstrate the ability to see
the following objects:
Colored lights of other aircraft in the vicinity
Runway approach lights
Airport boundary lights
Taxiway lights
Red warning lights on such areas as TV towers,
high buildings, or stacks
Conventional signal lights from the control tower
All color signal lights normally used in air traffic
control (ATC)
(5) AAM-300 usually requires that applicants
who have defective color vision take the signal light test
(SLT) to obtain second- and third-class medical certificates.
If possible, the test should be given at twilight to
test the applicant under both daylight and night conditions.
Under such special arrangements, the night-time
portion of the test may include tests other than those
described, such as identification of aircraft, runway,
threshold, and taxiway lights. Applicants who are able to
identify colors at night may have the night-time restriction
removed.