Graphlan heatmap legend

Dear all,
I am wondering how to add a heatmap legend scale, similarily to functions such as R heatmap.2.
For example in the tutorial there are two outer heatmap rings, colored with ring_alpha
Bacillaceae.Bacillus.Blicheniformis ring_alpha 2 0.570138625829

Is there a way to transform ring_alpha color values into a legend color bar ?

Best, Michael