Line A is calculating the spread between the Bid Volume - Ask Volume. Line B is a 50 period Exponential average of the Line A spread.
Line C adds 50 to the average and takes the Absolute value of the result. Line D finds the highest value from line C in the last 100 values, and this will be used as a divisor on Line E to calculate Average / Max Value.

Line B initialize the paint can with a default Blue color. Line F will test to see if the Line E ratio is above 0.5 and change the paint can color to Green.
Line G will test to see if the Line E ratio is below -0.5 and conditionally change the paint can color to Red.
Finally, Line H will plot the Line B average spread using the histogram marker and the color in the paint can. The paint can color will be used because the color selection for Line H is black. Black is the selection that tells the DYO to use the color in the paint can, which is either blue, green or red.

Sincerely, Howard Arrington