So... not just a headache. People who are susceptible to migraine have different visual perception *all* the time, and are made actively uncomfortable by things like flashing lights (which can trigger headaches) and high-contrast patterns on floors, walls, clothing, visual clutter, etc. The original rainbow flag, colors next to related colors, was not very high-contrast, and OK to look at. The newer versions are a total nightmare, and if I had it, say, as a desktop background, or something hanging prominently in my workplace where I'd have to see it a lot... probably a migraine trigger.