In 2008, the Americans with Disabilities Act Amendments Act (ADAAA) was signed into law and became effective on January 1, 2009. The ADAAA made a number of significant changes to the definition of “disability.” The changes in the definition of disability in the ADAAA apply to all titles of the ADA, including Title I (employment practices of private employers with 15 or more employees, state and local governments, employment agencies, labor unions, agents of the employer and joint management labor committees); Title II (programs and activities of state and local government entities); and Title III (private entities that are considered places of public accommodation).
In recent cases, the U.S. Department of Justice has repeatedly sided with plaintiffs arguing that a private company’s website needs to be accessible, despite any other mitigating factors. One thing is for certain, however: The number of federal lawsuits alleging violations of the ADA is currently accelerating at a rapid pace. Between January and August 2017, there were 432 ADA lawsuits filed in federal court—more than the total number of ADA lawsuits in 2015 and 2016 combined.
The Supreme Court decided under Title II of the ADA that mental illness is a form of disability and therefore covered under the ADA, and that unjustified institutional isolation of a person with a disability is a form of discrimination because it "...perpetuates unwarranted assumptions that persons so isolated are incapable or unworthy of participating in community life." The court added, "Confinement in an institution severely diminishes the everyday life activities of individuals, including family relations, social contacts, work options, economic independence, educational advancement, and cultural enrichment."
Aloha Tatiana! I wish your questions had straightforward easy answers – and if you are government funded it kind of is. (See here: https://www.ada.gov/websites2_prnt.pdf) if you are not government funded, this is something that is currently being debated in the legal system. That being said, the WCAG 2.0 guidelines are a good set of guidelines to help protect yourself if you feel you should. (You can see more on WCAG here: https://www.yokoco.com/find-out-how-to-make-your-website-compliant/)
UPDATE: Since writing this post in August 2017, several important changes have taken place in the laws regarding ADA compliance for websites. On December 26, 2017, the Department of Justice announced that they have withdrawn the Obama-era Advance Notice of Proposed Rulemaking mentioned in this article which intended to require ADA website compliance. The DOJ’s withdrawal announcement stated, “The Department will continue to assess whether specific technical standards are necessary and appropriate to assist covered entities with complying with the ADA.”
Distinguishable: To assist color-blind users and those with other visual impairments, color is never used as the sole means of conveying information or prompting the user. Audio lasting more than 3 seconds can be paused, or the volume can be controlled independently of the system volume. Regular text has a contrast ratio of at least 4.5:1, and large text has a contrast ratio of at least 3:1. In addition, text can be resized up to 200 percent without causing issues with the website.
As a result, most ADA suits are brought by a small number of private plaintiffs who view themselves as champions of the disabled. For the ADA to yield its promise of equal access for the disabled, it may indeed be necessary and desirable for committed individuals to bring serial litigation advancing the time when public accommodations will be compliant with the ADA."
While legal considerations might be your biggest worry, making your site more accessible is simply good customer service. More than 39 million Americans are blind and another 246 million have "low vision," Another one million are deaf in the U.S. Add to that people with mobility issues that prevent them from using their hands and that's a huge portion of the country's buying power.