I do not have time to make a dark skin (changing dll and fixing the desktop white problem) and I’m not going to make a dark skin template. But before prototyping is better to visualise the final result. Here is an example of how a Rhinoceros 7 can be (I invert and desaturate a Rhino5 screenshot in Photoshop).
Unity software is free but dark skin is a payment-optional that capture a lot of pay users. They pay just for the dark skin. I use both dark and light grey. In Rhino there are a lot UI of empty spaces. Unity fix very well that. I do not like distracting colours in icons. Is better to conserve the icon yellow colour that reference to selection. And grasshopper colour much Rhino. My workflow is Photoshop Rhino Blender Painter Unity and Rhino is the only one that is still light grey. Rhino starts looking like an advanced 90s tool and I like it how it is.
At the moment I prefer if Rhino put more effort into more useful mesh retopology options for exporting to Painter FBX game development rather than black skin.