I think both options are possible.
To move the yellow circles to the back,
you can right-click on the dimension on your color
shelf, select Sort, and then move the one in question
to the bottom of the list. Alternatively, you can go
to the Color Legend and move the yellow circle
to the bottom.
This may be overdone, but you could also try a dual axis graph
in which only the yellow circle dimension is on the second axis.
You could then change the opacity for only that axis.
Please see workbook v10.3 attached in the Forum Thread.
277364marks.twbx 1.3 MB