Welcome,
Sorry, it isn’t possible to switch between JSGF and ARPA in the same listening loop. They have two different kinds of structures that are established at the beginning of the loop and it can’t be changed on the fly without restarting all of the significant features of the loop, so this would require sending stopListening and then starting again with the new format. What is the reason for the requirement to take color input using ARPA instead of switching to a JSGF with RED, GREEN and BLUE?