I agree with basi that Transparency works fine here. I tried a few of those skins. Lets just use Diamond. Look at the SS. I see it for a lot of transparency so you can see it clearly works. It works no matter where I move the top slider which is the only one I ever use to adjust this.
I wanted to report this because I'm also on the older version of windows 1803. Same as you. Using same version of Start 10. I was using WB version 1065 and trans worked fine. I just now updated to the latest version 10.74 and it still works fine.
Can't answer why it doesn't work on your end, but wanted to let you know I have same version except for WB. I would suggest you update to the latest version of WB and see if that solves your situation as 10.74 works fine on Win 1803. Yes, I'm well aware you know your way around SD programs. Just trying to let you know I'm using the same Win 10 version. PS: I'm showing the Diamond WB.