envNoColor method
EnvNoColor returns true if the terminal should not emit colors based on
the environment. NO_COLOR wins; CLICOLOR=="0" requires CLICOLOR_FORCE
to flip back on. Piped stdout also forces no-color.
Implementation
bool envNoColor() {
if (_b.env.containsKey('NO_COLOR')) return true;
if (_b.env['CLICOLOR'] != null || isColorForced) return false;
return !hasOutputTerminal;
}