UX/Accessibility: Ensure that category colours have sufficient contrast

The "fun/culture" category at KIF-KoMa 2025 was shown in yellow on the AK wall, which lead to poor readability when projected in bright rooms. It would be useful to check category colours against an accessibility standard (e.g. https://www.w3.org/WAI/WCAG22/Understanding/contrast-minimum, though I am no expert on that).