Function detectFromColorFgBg

src/utils/systemTheme.ts:109–119

* Read $COLORFGBG for a synchronous initial guess before the OSC 11 * round-trip completes. Format is `fg;bg` (or `fg;other;bg`) where values * are ANSI color indices. rxvt convention: bg 0–6 or 8 are dark; bg 7 * and 9–15 are light. Only set by some terminals (rxvt-family, Konsole, * iTerm2 wit

()

 * iTerm2 with the option enabled), so this is a best-effort hint.
 */
function detectFromColorFgBg(): SystemTheme | undefined {
  const colorfgbg = process.env['COLORFGBG']
  if (!colorfgbg) return undefined
  const parts = colorfgbg.split(';')
  const bg = parts[parts.length - 1]
  if (bg === undefined || bg === '') return undefined
  const bgNum = Number(bg)
  if (!Number.isInteger(bgNum) || bgNum < 0 || bgNum > 15) return undefined
  // 0–6 and 8 are dark ANSI colors; 7 (white) and 9–15 (bright) are light.
  return bgNum <= 6 || bgNum === 8 ? 'dark' : 'light'
}