Locked solid object - how to change transparency?

How can I change a setting on my computer to make a locked solid object transparent so I can see my original poly line and control points.
I went to Rhino - Preferences- colors. Changed the color of locked object and changed Opacity, then pressed Apply. Nothing changed. The Opacity setting just went back the way it was.
What other tools are available to accomplish this?

Hello - that is set per display mode -


Thank you Pascal… Yes, this is on your PC… I need directions for mac

Hi -

This is how it looks on the Mac:


thank you so much