I was going through some settings in eM Client and I noticed a theme editor. Apparently you can also save your themes.
I’m curious to see what others have as their themes and if there is a place where other users can add their contributions so others can download?
eM Client created recently a page on their server to host user created themes:
Custom Themes from Our Users
Thanks, there’s a few there. Unfortunately, there’s no way to delete a theme after you installed it into the client. I accidentally downloaded two of the same, now I want to delete one.
It is not clear, but there is a way:
Highlight the theme and hit the Delete key on your keyboard. 
Lol. Thank you. I guess someone forgot to add the delete button,
They presumed you got one on your keyboard! 
I remember commenting some years back that I frequently found instances where it was not obvious how to do something. And this is a good example of that, which I only discovered last month, thanks to @cyberzork, that the Delete key served it’s intended function here.
I am not sure that they forgot to add the button, or it was by deign. Fortunately I have noticed that they seem to be improving in this area of design.
Ha. Yes. I was just trying to change some basic views (colors) like the day of the week with the light grey blends in way too much that it makes it difficult to see. While the Theme Editor has a “pick” feature, I think it’s more or less useless because it doesn’t allow you specify exactly what you want to pick, the changes are not in real time, and the names of the field choosers are far, far from intuitive or common.
While the customization of Themes is certainly a big bonus, it’s not for most people. And judging by the limited themes and how they’re created, it’s not a commonly utilized feature.
I couldn’t have said it better.
When I first started using eM Client, I experimented with a few themes, but in the end the default Modern Theme was all I needed.