Web design over time has gotten less and less connected to accessibility & utility, and more and more connected to what might look good in a screenshot. Use of color is but one egregious example.
There are real, accessibility-based reasons to make sure all of these things are configurable and the configuration sticks, but there shouldn’t need to be. When a web designer decides that his own sense of aesthetics matters more than the decisions of the user, a false division is created. The web designer should not be the master in this relationship; the web designer serves the user, and should bow to whatever any user prefers, to the extent possible. This is not the way things work now; instead, web designers act as arbiters of taste, with major consequences for large groups of people.
Most websites are essentially unusable for the blind or those with major vision problems — and for those of us with vision within the normal range, these websites are merely irritating. The average size of a website is approaching the size of the original shareware release of DOOM — in other words, if your machine is old, or your connection is slow, most sites are again unusable. A dyslexic person may want to set their font to one of the many fonts designed to change bilateral symmetry in order to improve the ease with which letters can be distinguished; CSS tricks are used to disable user-selected default fonts, and when user-selected fonts happen to show through, the sizing, layout, and behavior of the website is negatively affected because the designer has home-brewed a fragile system for implementing controls and layout rather than using standard widgets and sensible defaults.
A website is not an art project; a website is a piece of machinery that people accept into their lives, like an appliance. Just as nobody would accept a microwave that exploded if you tried to heat up pizza in it rather than baked potatoes, nobody should accept a website that ceases to function when the font is changed. Just as nobody would accept a stool that is nailed to the floor and cannot be repainted, nobody should accept a website that doesn’t respect a user’s color and size preferences. Just as nobody would accept a vaccum cleaner the size of an elephant, nobody should accept a website that takes ten megabytes to serve up 500 words of text.
A false idea of expert difficulty prevents people from demanding these things from the sites they visit. This idea is false not because modern web design isn’t complicated — modern web design is very complicated, and you really do need to be an expert to practice it. Instead, this idea is false because the only things in web design that are really difficult to do are things that should only be done rarely, if at all. The web is optimized for transmission of large chunks of minimally-styled text; using it to simulate native applications, while impressive, is a terrible idea and should never have become normalized.