Per review on #1715 (nits 3 & 4): the BT.709 relative-luminance + #rrggbb parsing was duplicated three ways (session-color relativeLuminance, theme bgIsLight, isLightTheme), and each rejected #rgb shorthand via length !== 7 — so a custom theme using shorthand backgrounds silently kept the washed-out accent. Lift it into utils/color.ts hexLuminance() (accepts #rgb and #rrggbb), route all three call sites through it, and add tests.
Paweł J. Wal
4856c1dd3b