Check out agnostic-dark-syntax.
I love Atom and have been using it as my primary text editor for a long time. I bounce between syntax themes for my code every few months. I like colour in my code, but not too much, so the default theme One Dark and some of the popular choices like Monokai are too bright for me.
For a while I used Behave but I again felt that there was too much going on. Then I settled on Eclectic.
I really love the Eclectic theme but had a few issues with it — some background colours seem off when you open Atom's settings, and there is a little too much colour when opening HTML files.
So I grabbed most of the colours from Eclectic, shifted some values around, and plopped them into a forked version of Atom's default theme, One Dark.
I call the result Agnostic Dark, and I hope you'll give it a try. It supports most languages pretty well.