Green: Trades at the inside Ask Red: Trades at the inside Bid White/Gray: Trades in between the inside Bid/Ask Yellow: Trades above the inside Ask Purple: Trades below the inside Bid Grey Highlight: Inside quote change. Not a transaction.
Look at the bid and ask at time of trade...right in between 12 bid and 14 ask...
Here this is more of what you were asking...it is considered black
Green = Buy Red = Sell Black = Unknown trade volume as it was done between the Bid/Ask. The Buy, Sell and ? Volume columns represent a daily running total of quantities for each type of trade.