You can get a pretty wicked good looking plastic with dielectric, but not if you want it with a Milky look. That requires at least some fake SSS so that you send light in , and you can control sending light back toward the camera.
The Cloudy plastic is Great for that. Only, it's missing a Huge setting. Ever seen a really milky plastic that has the exact same roughness on the inside as the surface? No. Hardly Any materials are like that. That's what is so great about the dielectric material.
I ended up settling on using the translucent material. This part is probably a 4mm ring about 25mm wide. That's it. And I had to use a translucency distance of 1000mm to get close to what i wanted. It's not correct, but if it looks good, it is good. After it finally cleared up enough, and denoise is Necessary, it ended up too dark but that's an easy photoshop fix. At least it's one render submition.
I was trying to figure out a way to put a clear coat on the cloudy plastic. Because that has the controls I want. All, except for some surface reflections. And yeah, I can render twice. But I have a lot of views and color versions to do. So that is Really not ideal. Do you know how long it takes to send 18 different studios to a network farm from home to work? Because I do. Cutting that in half is definitely worth it.
I thought I had something working with transparent plastic as a label. I'm not sure why it lets you do that, but doesn't let you use some of the other transparent materials, but it seemed pretty messed up. I Really wish Keyshot just had Real material mixing. Labels are super nice, because it's quick. But sometimes you just need an advanced material.
So milky plastic, but with a nice gloss finish. Ideally, using the Cloudy Plastic. And there are details Right behind this thing. Internal glossy needs to be somewhere between .2 and .3 at minimum. There's no light on the other side, so all the light is from the front. There are LED's back there, but they won't be turned on....for now. (Ha, I'm not wasting my time with that. I do that in Photoshop 99.99% of the time)