running into the same issue, brand new BrickPi (says v2.8 on board, firmware version returns 2).
ColorSensor-LED lights up in selected color if using specified color mode (Red, Green, Blue), but not when going for FullColor mode.
It does start working however (all 3 colors light up, haven’t examined returned values) when using the workaround found described earlier and configured port3 (where CS is attached) and port4 together for a color sensor (see http://www.dexterindustries.com/topic/problems-with-lego-color-sensor/ )
Given for FullColor mode, a much wider return value is used, and the workaround does not work if using Port 4 (or 2), I almost suspect some memory location may be out of range.
Or might be an timing issue, setting up the CS results in a timeout on my receiver side on the RPI, while all other sensors (original NXT2, some HiTechnic) work well so far. Don’t have a logic analyzer at hand to verify timings, At least I can exclude the timing issue between RPI and BrickPi, this part works reliably now after some more work, I missed the fact the CS needs somewhat more time to initialize.
Remains the issue as per above that initialization needs to be done on both port of the same Arduino, and only works if the CS is attached to the first of those ports, so my gut feeling is some address issue in the firmware for CS & FullColor mode.
If someone has an idea how to track that further down, ideas are welcome. Would be great to see this issue solved on BrickPi, also given it’s an ongoing issue for more than 2.5 years already (as per thread above and this other thread http://www.dexterindustries.com/topic/brickpi-colour-sensor/).
Maybe DI take one of the retail BrickPI kits with preinstalled FW to debug, if you else can’t recreate the issue else (with your dedicated debug board & FW??!)?