You would show whatever the aircraft thought the stick was doing. So if pilot A was pulling back and pilot B was pushing forward, the little glowing dot would indicate whatever the aircraft had picked out of the two inputs and understood. Either pilot would be able to see that they were not the only person making inputs, if the little dot was doing something other than reflect the inputs they knew they were making.
You could perhaps add a red dot overlaid by the white, that showed you what input the aircraft had 'allowed', if a pilot was hauling back on the sidestick for all they were worth and the computer was saying 'no you don't, I'm pushing forward...' for some reason...