Consider "transparent" in charting color pallet

This request is to enable a color selection to be transparent in dashboard stacked bar charts. What this enables is the summing of multiple SUM or Count terms to render the final value graphically. A normal stacked bar seemingly would achieve this, but if any of the terms are negative, the display does not reflect the correct term summing result. Solution is to create a final term to the function of prescribed minimal amplitude, and that being the only one with a non-transparent color.

This gives considerable expanded functionally to charting in that multiple plus/minus terms can be combined to chart the final summed results.

Thanks for consideration.
Regis

Just for reference - go and upvote by clicking the :+1:
https://github.com/metabase/metabase/issues/5763

flamber pertinent to question of summing terms when some are negative, use of calculated fields and custom foirmulas does not work since there is no conditional ability in either. since my summing of a record value is determined by the value 1 to 3 of a record.type field, I’m afraid that even use of combination of these two Metabase features will not give me the answer.

thanks for trying to help.
Regis