color: check if ui is already a subclass of colorui before wrapping it since it's possible to reuse the ui object (see 80c599eee3f3) between dispatch calls, the ui might have been wrapped already. we could probably move this test up a bit but leaving it here allows updates to take effect by extstyles() and configstyles().

util: add helper function isatty(fd) to check for tty-ness