Make color variables global instead of it being per-terminal.

grub-core/kern/term.c

@@ -28,6 +28,10 @@ struct grub_term_input *grub_term_inputs_disabled;
 struct grub_term_output *grub_term_outputs;
 struct grub_term_input *grub_term_inputs;
 
+/* Current color state.  */
+grub_uint8_t grub_term_normal_color;
+grub_uint8_t grub_term_highlight_color;
+
 void (*grub_term_poll_usb) (void) = NULL;
 void (*grub_net_poll_cards_idle) (void) = NULL;