Web designers often design in such a way that does not allow the user to adjust font size or color. While they may be protecting their brand, they are also inhibiting some users. Many visually impaired need to use high contrast color settings or very large fonts to read a website. Don't design your website in a way that makes it impossible for them to do this. 

The Department has assembled an official online version of the 2010 Standards to bring together the information in one easy-to-access location.  It provides the scoping and technical requirements for new construction and alterations resulting from the adoption of revised 2010 Standards in the final rules for Title II (28 CFR part 35) and Title III (28 CFR part 36).
The U.S. Department of Transportation enforces regulations governing transit, which includes ensuring that recipients of federal aid and state and local entities responsible for roadways and pedestrian facilities do not discriminate on the basis of disability in highway transportation programs or activities. The department also issues guidance to transit agencies on how to comply with the ADA to ensure that public transit vehicles and facilities are accessible.
As of 2015 the ADA had improved access to public services, the built environment (e.g., crosswalks with curb cuts and accessible pedestrian signals), understanding of the abilities of people with disabilities, established a right to equal access to public services and has demonstrated the contributions which people with disabilities can make to the economy. Disparities have remained in employment, earned income, Internet access, transportation, housing, and educational attainment and the disabled remain at a disadvantage with respect to health and health care.[45]
Many people with disabilities use assistive technology that enables them to use computers. Some assistive technology involves separate computer programs or devices, such as screen readers, text enlargement software, and computer programs that enable people to control the computer with their voice. Other assistive technology is built into computer operating systems. For example, basic accessibility features in computer operating systems enable some people with low vision to see computer displays by simply adjusting color schemes, contrast settings, and font sizes. Operating systems enable people with limited manual dexterity to move the mouse pointer using key strokes instead of a standard mouse. Many other types of assistive technology are available, and more are still being developed.
However, in states that have enacted laws that allow private individuals to win monetary awards from non-compliant businesses (as of 2008, these include California, Florida, Hawaii, and Illinois), "professional plaintiffs" are typically found. At least one of these plaintiffs in California has been barred by courts from filing lawsuits unless he receives prior court permission.[55] Through the end of fiscal year 1998, 86% of the 106,988 ADA charges filed with and resolved by the Equal Employment Opportunity Commission, were either dropped or investigated and dismissed by EEOC but not without imposing opportunity costs and legal fees on employers.[50]
I know there may have been concerns that the ADA may be too vague or too costly, or may lead endlessly to litigation. But I want to reassure you right now that my administration and the United States Congress have carefully crafted this Act. We've all been determined to ensure that it gives flexibility, particularly in terms of the timetable of implementation; and we've been committed to containing the costs that may be incurred.... Let the shameful wall of exclusion finally come tumbling down.[41]