When I place a stone on a person's body, perhaps I do so in trying to bring a higher octave of a color that the person needs to that area. I think that when you stop looking at a person just in the physical range, that their chakras etc. can be any color, not just the ones consensually associated with that spot. Accompany it with your mind without emiting a sound. I have a toning bar in the note of E. The card with it said that birds sing in the note of E at dawn. The trees respond to their song - sap begins to rise and prepare for activity under the new days sun.
Natures wake up call.
E is my favorite note. My son hurt his arm and our cat lay on it and purred. I've heard such sounds and I can't yet make them here. Once someone was doing a healing with me and he sang over my spleen a very harmonicy sound. Suddenly I could see my spleen and it was being filled with buzzy energy.