To get an object in sculpt mode to be transparent in 2.8, I was doing this:
Set Viewport Shading to Solid (Icon to the right of the wireframe icon). Click the Object. Go to Material Properties. Click ‘New’. Scroll down to Viewport Display & click Color. Adjust the ‘A’ (which stands for Alpha) value.
It was working great, again and again until I couldn’t get it to work again. Some global setting must have changed. Any suggestions about what I’m doing wrong?