The ADA has two main areas - public accommodations and employment

Public accommodations means those places and services that are offered to the general public - stores, offices, stadiums, etc. Employment is self explanatory.

The public accommodations provisions are geared towards the populace as a whole and are set forth in the regulations written under the ADA. For example, sidewalks are required to have wheelchair ramps and the regulation sets out the exact requirements for a wheelchair ramp. There are no specific provisions in the public accommodations regs for color blindness.

Unlike public accommodations, in employment the ADA is directed as the specific person with the disability and the specific job in question. Disability under the ADA employment means a substantial impairment in a major life activity. This is defined in a case by case basis. With the so-called minor disabilities (such as colorblindness, night-blindness, inability to stand for long periods, weakness) whether a person is considered disabled is a tough question which could be decided either way.

If the person is considered disabled under the ADA the next question is can the person perform the essential elements of the job with a reasonable accommodation by the employer.

I am aware of one case where a person sued under the ADA employment provisions. In Shannon vs. New York Transit, a colorblind man wanted to be a bus driver but the city fired him because he was colorblind. The court was ambiguous as to whether colorblindness qualified as a disability, it ruled that the man could not perform the essential elements of the job because identifying traffic lights was an essential element of the job which he couldn't perform with a reasonable accommodation.

Likewise a truck driver with night-blindness and a nearsighted airline pilot lost their cases.