The Buy/Sell line add-on is located first on the Strategy Bar.
There are four options to add the 50-day simple moving average:
50 Period SMA: When the box on the left is checked the 50 SMA line will be added.
Background: When the box on the left is checked the 50 SMA will be added as a background.
Color Ribbon: When the box on the left is checked the 50 SMA will be added as a ribbon on the bottom of the chart.
Fluid: When the box on the left is checked the 50 SMA will be added as a fluid.
What do those colors mean?
The blue color is for when the price is above the 50 SMA and the red color is when the price is below the 50 SMA.