Green, or ? trades seem to always happen on 0.0001 trades that occur after a bid/ask of 0.0001 x 0.0002 drops back to no bid x 0.0001.
My dumb guess is that the system doesn't know if someone trying to sell a bunch of 0.0001s wasn't able to sell them all (because it went to no bid), so it doesn't know whether to register the trades as a buy or sell?
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