109 (PC) Black IR
Status: Current (?)
This color looks dark, but lets infrared (IR) pass through. Useful for remote control parts. PC presumably stands for the plastic (PolyCarbonate), which is the same as most transparent parts.
I'm actually not sure which part here is this color! They're all slightly different; the PF receiver is like a dark trans purple, the RCX transmitter is a dark translucent bluish, and the piece from the RCX itself (bottom right) is quite opaque, with a red color when lit from behind with a very bright light.