If you have ever searched for open source keyboards, you might have come across OpenBoard. But that project hasn’t seen development in more than an year. Thankfully, there is a fork of it that is being worked upon quite actively. It already supports autocorrect, glide typing, user-defined dictionaries, multilingual typing and now material you themeing as well.
Well maybe the image above doesn’t look good for you, but for me it does look fine, it is similar to how I have Gboard right now.
About the green yeah I can agree, at least you can tweak the colors whether it is rom side or with an app as mentioned above.