No, there is no built-in function for this. Calculated fields are the key.
What I usually do in this type of situation is to create a chart which becomes the legend. In the attached example using the Superstore database, I use the Category dimension, but you could just as easily use your calculated field.
Bar chart as legend.twbx 1.2 MB
As Bill recommended,
I suggest a minor improvement to the Bar chart legend:
1.- Show Mark Labels
2.- Remove Show Header from x-axis
3.- Add a filter or highlight action from bar chart view to related views on the dashboard