Here is how the FAA handle the colour vision issue. It is very fair and they have a large body of both medical and real world flight experience to support their position in regard to this issue.
My case was straight forward. I failed the ishihara test and my AME recommended that I go for the signal light test. I passed and was issued a SODA valid for all classes of medical. When I returned to renew my medical The AME had a shiny new Titmus vision tester. To everybodys surprise I passed the Colour plates on this machine (ishihara plates, but mounted at the correct distance and properly lighted) this was then confirmed when I passed the Farnsworth Lantern. The FAA are in the process of removing my SODA and replacing it with a letter that states that I meet the standards without the need for a waiver. this is important for professional job applications, needless to say I am chuffed about this development.
All well and good I suppose but oh if it were only that simple, I am Irish and would like to return and get a JAA licence. I had a go at the Holmes wright lantern but failed so my battles with the IAA/JAA are only begining. That is something for another post however but here are the details on what is acceptable to the FAA
Color Vision
(Attachment for Procedure for removal of color vision restriction)
CODE OF FEDERAL REGULATIONS
All Classes: 14 CFR 67.103(c), 67.203(c), and 67.303(c)
***ability to perceive those colors necessary for the safe performance of airman duties.
EXAMINATION PROCEDURES
Equipment
Pseudoisochromatic plates. (American Optical Company [AOC], 1965 edition; AOC-HRR, 2nd edition; Dvorine, 2nd edition; Ishihara, 14-, 24- or 38-plate editions; or Richmond, 1983 edition, 1 5-plates).
Acceptable substitutes:
Farnsworth Lantern
Keystone Orthoscope.
Keystone Telebinocular.
LKC Technologies, Inc., APT-5 Color Vision Tester.
OPTEC 2000 Vision Tester (Model Nos. 2000PM, 2000PAME, and 2000PI).
Titmus Vision Tester.
Titmus 11 Vision Tester (Model Nos. Tll and TIIS).
Titmus 2 Vision Tester Model Nos. T2A and T2S).
Techniques
The test plates to be used for each of the approved pseudoisochromatic tests are: Test Edition Plates
AOC 1965 1/15
AOC-HRR 2nd 1/11
Dvorine 2nd 1/15
Ishihara 14-plate 1/11
Ishihara 24-plate 1/15
Ishihara 38-plate 1/21
Richmond 1983 1/15
The following conditions should be ensured when testing with pseudoisochromatic plates:
The test book should be held 30 inches from the applicant.
Plates should be illuminated by at least 20-foot candles, preferably by a Macbeth Easel Lamp or a Verilux True Color Light (F1 5T8VLX).
Three seconds should be allowed for the applicant to interpret and respond to a given plate.
Testing procedures for the Farnsworth Lantern; Keystone; LKC Technologies, Inc.; OPTEC 2000, Titmus, Titmus II, and Titmus 2 Vision Testers accompany the instruments.
The results (normal or abnormal) should be recorded.
DISPOSITION
An applicant does not meet the color vision standard if testing reveals:
All Classes
Seven or more errors on plates 1-15 of the AOC (1965 edition) pseudoisochromatic plates.
AOC-HRR (second edition): Any error in test plates 7-11. Because the first 4 plates in the test book are for demonstration only, test plate 7 is actually the eleventh plate in the book. (See instruction booklet).
Seven or more errors on plates 1-15 of Dvorine pseudoisochromatic plates (second edition, 15 plates).
Six or more errors on plates 1-11 of the concise 14-plate edition of the Ishihara pseudoisochromatic plates. Seven or more errors on plates 1-15 of the 24-plate edition of Ishihara pseudoisochromatic plates. Nine or more errors on plates 1-21 of the 38-plate edition of Ishihara pseudoisochromatic plates.
Seven or more errors on plates 1-15 of the Richmond (1983 edition) pseudoisochromatic plates.
Farnsworth Lantern test: An average of more than one error per series of nine color pairs in series 2 and 3. (See instruction booklet).
Any errors in the six plates of the Titmus Vision Tester, the Titmus II Vision Tester, the Titmus 2 Vision Tester, the OPTEC 2000 Vision Tester, the Keystone Orthoscope, or Keystone Telebinocular.
LKC Technologies, Inc., APT-5 Color Vision Tester: The letter must be correctly identified in at least two of the three presentations of each test condition. (See APT-5 screening chart for FM-related testing in instruction booklet).
Certificate Limitation
If an applicant fails to meet the color vision standard as interpreted above but is otherwise qualified, the Examiner may issue a medical certificate bearing the limitation:
NOT VALID FOR NIGHT FLYING OR BY COLOR SIGNAL CONTROL.
Special Issuance of Medical Certificates
An applicant who holds a medical certificate bearing a color vision limitation may request reevaluation or a SODA under the special issuance section of Part 67 (14 CFR 67.401). This request should be in writing and should be directed to the Aeromedical Certification Division, AAM-300. If the applicant can perform the color vision tasks, the FM will issue a medical certificate without limitation with a SODA.
Demonstrating the ability to perform color vision tasks appropriate to the certificate applied for may entail a medical flight test or a signal light test. If a signal light test or medical flight test is required, the FAA will authorize the test. The signal light test may be given at any time during flight training. The medical flight test is most often required when an airman with borderline color vision wishes to upgrade a medical certificate.
X-Chrom Lens
This lens is not acceptable to the FAA as a means for correcting a pilot's color vision deficiencies.
Yarn Test
Yarn tests are not acceptable methods of testing for the FAA medical certificate
Note that the FAA list of acceptable tests is rather long, this is a direct result of their experience with this problem. A lot of people are on the borderline with this problem and if you can pass one of these tests they will be OK and even if you can't then the signal light test is still an option.
following is another post with details of the signal light test.
Good luck