In the main properties you set your trade and trade background colors. These are used as the two extremes of the fade as well as in other areas of the frontend.
In the contract window properties there are two settings that will affect how these bars are displayed. Fade Time is the number of minutes that it takes to fade from one extreme to the other. Prop Scale is a scaling factor used to adjust the width of the bar.
Each price level operates independently from the others. If a trade occurs then time is set to zero and the color associated with time = zero is applied. Then as time elapses toward the fade time value the color is faded smoothly to the color associated with time = fade time.
