private static void set(int idx, Operation o) {
        switch (idx) {
            case 0:
                VIOLET.setOperation(o);
                break;
            case 1:
                INDIGO.setOperation(o);
                break;
            case 2:
                BLUE.setOperation(o);
                break;
            case 3:
                GREEN.setOperation(o);
                break;
            case 4:
                YELLOW.setOperation(o);
                break;
            case 5:
                ORANGE.setOperation(o);
                break;
            case 6:
                RED.setOperation(o);
                break;
        }
    }