Forced Colors & High Contrast
Operating systems let people swap every color for their own palette (Windows High Contrast / `forced-colors` mode). Don't fight it: use semantic HTML, keep meaning out of background images, and check that content still reads after the swap.
Some people replace every website color with their own high-contrast set. Build so your site still makes sense when they do.
Why this matters
Many low-vision users run Windows High Contrast or forced-colors mode, swapping every color for their own palette. Designs that bury meaning in background images or fixed colors fall apart for them.
How to detect
Turn on Windows High Contrast (or emulate forced-colors in DevTools). Is all content and every control still visible and usable? Watch for vanishing icons, borders, and text set over images.