I mocked up something, but I'm not sure if it meets your requirement.
Basically, it separates Value into CO and CO2, and then pulls up the
appropriate value when Selected.
In the attached example the high is 6 for CO and 25 for CO2.
Did you want 6 to be associated with the darkest green for CO,
or did you want the darkest green always to be associated with 25?
Also, were you seeking to change to a completely different color upon selection?
210215color.twbx 11.4 KB
Your workbook looks interesting. I wanted to use same colormap, but just change the center point (Edit Colors > Advanced dialog) for each variable. Having custom start/end points is also acceptable.
I opened your workbook in Tableau reader, but can not see how you made it. Can you tell me what you did?
My data is set up as Type (CO,CO2), Value.
I have a parameter [SelectType].
CO values are in [CO]:
IF [Type]="CO" THEN [Value] END
Likewise for [CO2]:
IF [Type]="CO2" THEN [Value] END
I filter the data to whatever is selected:
IF [Type]="CO" THEN [CO]
So when [SelectedValue] is placed on the color shelf,
the range will only be that of CO or CO2.
So in this scheme, the darkest green will be the highest value
of whatever is selected.