Earlier pass tried %X17 (256-palette idx 23), but %X isn't the 256-colour code in modern irssi — 1.4+ treats %X as a no-op for unknown sequences, so every intended teal element was silently falling through to the terminal default (= bright white). irssi 1.4.5 supports %Z<rrggbb> for 24-bit foreground colour, so use it directly: %Z005f5f renders as exactly #005f5f (dark teal), no palette guessing.