A method implemented on a data processing device is described comprising: generating supplemental data defining one or more characteristics of one or more light-emitting diodes ("LEDs") on the data processing device; embedding the supplemental data within a musical instrument digital interface ("MIDI") stream; decoding the supplemental data concurrently with decoding the MIDI stream; and modifying the one or more characteristics of one or more of the LEDs responsive to decoding the supplemental data.