Node of USN uses the radio, similar to the RFID, for the transfer of messages. Thus to deliver query to a closely located node, it shall be moved via many hops considering limited power. However if there are many unknown nodes located in users' vision, the physical contact and indirect method by hop are both insufficient. Thus as a flash may be used to find a key in a darkness, a more direct and short range communication system is required.This study shall resolve such question through 3 different steps. First a hardware module, which may deliver various LED color signal, shall be developed. Second a color coded transmit/receive protocol based on gray code shall be suggested. Third, relationship between signal frequency and recognition rates by controlling the experimental elements shall be found. The experiment may take place by fixing the entry angle of light and distance by setting a specific element as a standard mean.