Daniel - Very belated response. There are (possibly) two different things going on here.
Firstly, what am I trying to do?
This goes back to a problem I was having with a percussion player using multiple instruments (crash + sizzle + vibes) - and the full score was not showing the individual instruments. So my thought was to put a text box over the multiple instruments specification - and specify the individual instruments on separate lines inside the new text box. My hope was that the newly created text box would hide what was underneath. Now admittedly this is a very kludgy solution - especially since I would likely have to do it on each page of the score - but I was just experimenting.
As you can see from pic 1, you can see the text for the individual instruments, but the text box is not hiding what is underneath.
Changing Opacity does not work
My next thought was that my text box background was transparent and not hiding what ever was behind it. So I opened up the text box again, clicked on the background and changed the opacity from 100% to 0%. That is in pic 2.
But when I closed the text box, nothing changed. So I re-opened the text box to see if there was something else I could do, but when I clicked on the background, the Opacity was back to 100%. See pic 3.
Dorico appears to be ignoring my attempts to change the Opacity.
Daniel - I know that you guys are doing some intense development work on Percussion and perhaps this will be completely unnecessary in the next release - but I would still expect my changes to Opacity to work. Am I doing something wrong? Perhaps my text box is already in the back - and so Dorico is saying there’s nothing behind my text box to hide? If so, is there any way to move my text box in front?