This is a little tricky to explain over text...but here goes
Yellow line is a 2D representation of the market activity. If you had a candlestick chart you would see basically a 3D representation of market activity and thus more detail.
So.....
Yellow line is the final closing price for the time period drawn out as a line chart. This could be sliced in 1 minute increments, 5 minute increments and so on. (M1, M3, M5, M15, Etc) (Since we are using a line to represent the chart instead of candle sticks, you have to slice up time frames and select the last market trade.)
Green is all the completed buys above the "market closing" of the time frame. (this shows you how much trading was happening above the close price (yellow line)
Red is all the completed sells below the "market closing" of the time frame. (this shows how much trading was happening below the closing price.
Basically it is a line chart made to represent a candle chart by showing trading volume above and below the closing price.Damn...did that make any sense?...lol