jp: don't guess background when stdout is not a tty

sat_frontends/jp/base.py

@@ -120,6 +120,8 @@ class Jp(object):
         return config.getConfig(self.sat_conf, section, name, default=default)
 
     def guess_background(self):
+        if not sys.stdout.isatty():
+            return 'dark'
         stdin_fd = sys.stdin.fileno()
         old_settings = termios.tcgetattr(stdin_fd)
         try: