cl_airrollviz 1 to turn it on or
0 to turn it off.
The display turns green when analog directional air roll is used. It turns red when using the air roll toggle (default bindings). It is yellow whenever analog directional air roll is not being used, like when the input is 0 or 1, or when you're on the ground. You may find that it is yellow at value like 0.8 in the air. In that case, you are using an aerial sensitivity that causes the input to be effectively 1. (I am not just displaying the multiplied value because dodges will still use the unmultiplied value.)
This plugin was made so people using analog directional air roll can show it off and viewers can easily identify via the green color when it's being used. The red color for default air roll might also be useful to show off how different players use a combination of the two input methods.