When I watch the various "export from CC3 / import to Unity 3D" youtube tutorials...
The imported fbx model, looks practically exactly like it did in CC3.

Initially I made the mistake of dragging the FBX file that was exported into Unity 3d...
(Windows 10, Unity 3D 2019.3.x, HDRP project type, CC3 Auto Setup 1.2 for Unity 3D 2019.3.x)

The result (below) was rather horrific....

76% of original size (was 662x19) - Click to enlarge

Then I rewatched the tutorials....and found out that I needed to use the prefab, that was created in the prefabs folder by the Auto Setup script.


T76% of original size (was 662x19) - Click to enlarge

The result was much better (below)

76% of original size (was 662x19) - Click to enlarge

This is what I did in CC3.
I loaded a CC3 plus male character.
I used Headshot and generated the face/model from that.
Then went to Skin Gen.
Made the skin a little rougher.
Added some sweat to face skin.
Added some facial stubble.
Then exported the model to Unity3D/FBX file, using standard settings for exportation.

The above image was the result of importing to Unity3D.
The above image, left side of image is the Unity 3D prefab.
The above image, the right side is what it looked like in CC3.
Now I realize I may not get 100% the exact look, inside Unity 3D, from what it looked like in CC3...

But when I watch the video tutorials, it looks almost exactly the same way it looked like in CC3.
But my model looks like it needs tweaking to achieve this result..
Is there a tutorial or thread posting here, to show how to do this?
That uses SkinGen and CC3 plus format? (the video tutorials only deal with regular CC3 format not CC3 plus format).

Some comments..
1) The Unity3D hair VS CC3 hair....the CC3 hair is more slicker and nicer looking.

2) The Unity3D eyes/eyelashes are not as subtle looking as the CC3 eyes/eyelashes.

3) The CC3 skin has sweat and the skin is rough looking, the Unity3D version is more bumpy looking, and you don't really notice the subtle look of the sweat like it looks like in in the CC3 version.

One thing that helped me, and got rid of the green in your screen shot, was to setup my cc3 importer unity project to start with the unity HDRP sample project, and then not update the HDRP Pipeline version. (And not install HDRP via the package manager latest version into an existing project). Which in my case then the HDRP version in unity is 7.3.1. And I'm using unity 2019.3.15f1.

This is a daz figure (with daz skin texture) I brought through and did a little bit of skingen changes, and switched in the cc3 eyes instead of daz eyes. I haven't had enough time to work further with it but I did make some minor tweaks to the lighting in this default  sample project scene. Which I suspect lighting is going to have a big factor on how the characters are going to look in unity and the hdrp post processing config. Scene view, and game view through main camera:
76% of original size (was 662x19) - Click to enlarge

I'm still learning myself, so hopefully this helps

Even with getting the above scene working. I still was running into problems with trying to get rid of the green in other projects. So I take my CC3 importer project above, and export completed characters as custom asset packages, and then import them into whatever project I want.

If you are still battling the green. Another thing I found after a ton of tedious project settings and hdrp configuration comparisons between projects with it working vs projects with it not working. I eventually found problems with the HDRP Skin Diffusion Profile, which is referenced/linked inside the HDRenderPipelineAsset file (Project Settings, Graphics, Scriptable Render Pipeline Settings). Maybe this is some unity bug or what but, when I create a new project via the hub starting the project as HDRP, that default sample project /assets/settings/skin.asset file, has MORE yaml settings in it that are not displayed in the inspector gui, and are not present in skin diffusion profile settings files that get generated for me when I manually convert a project to HDRP via adding the package from package manager. Or maybe I was/am making some mistake with the manual workflow. When I was comparing the good/bad projects the inspector looked the same for the skin diffusion profiles. But when I compare the files themselves in text editor or merge tool, good/bad was very different. 

Hi all,

The green issue shall be fixed in Auto Setup v1.1. Diffuse map shall be applied correctly. 
https://www.reallusion.com/character-creator/unity-auto-setup.html

May you help to submit issue to Feedback Tracker?
https://www.reallusion.com/FeedBackTracker/
Thank you!