you can accomplish that by group the two mark category into one category then highlight on it ...
As I do not know your data let me describe it with super store data for example when click one mark 2 category selected ...
1- let us create the following calc field
if [Product Category] = 'Furniture' then 'G1'
2- Then I create two sheets
the first contain the category group as selector and the second contain sales colored by product category then display both in the dashboard like the below picture:
3- create highlight action that allow the highlighting from first two second sheet by selecting the group
as you can see I select the mark G2 and the red and blue lines are highlighted in the same time ...
Here is also the VIZ you can download it ...
So here's one way...
First I created a dummy dimension with the value '1'...I've called this (imaginatively!) [1One]
I bring this field into the detail pane of my viz....
I then set up the "control" sheet...like so (also with [1One] in the detail)
i bring these both into a dashboard (along with the legend), and set up the following highlight action
and now if I click on the control both are highlighted and the values show, or for the legend just a single year.
Hope that helps
Viz and Contol Show Values.twbx 305.8 KB