Follow the link to the data spec in post #1 and it states rather clearly No external resistor required, 6.0 volts @ 15 mA. So it has either an internal resistor or an internal current regulator. ALL the colors take 6.0 volts at 15mA. So the resistor for 12.0 volt use is 400 ohms, or use a 390 ohm (Orange white Brown) resistor and push the current a small bit.The TS wants to connect it to 12 volts. A.K.A. possibly an automobile. In which case, running a 6V LED on 12V will require additional resistance. However, one must take into account the Vf and internal resistance when adding an external resistor. Or am I the only one who took it that way?