You can't !!!
That's a curious limitation of the actual LV version, common to most 3D objects. There is a workaround : set the ring background color to invisible with the paint brush. Create a decoration, and place it UNDER the ring control. Then change the decoration color programmatically. See the attached vi...
CC
Chilly Charly (aka CC)
E-List Master - Kudos glutton - Press the yellow button on the left...