Neither MacOSX nor iOS offer to change the OS theme. If you want to do this, you need to use [third party software](http://mac.appstorm.net/roundups/graphics-roundups/20-stunning-themes-for-mac-os-x/).

What MacOSX does offer, is changing the color profile and calibrate it in **System Preferences -> Displays -> Color -> Calibrate**.

I've played around with different options and found the option **"Cool bluish white"** to be much easier on the eye:

![enter image description here][1]



  [1]: https://i.sstatic.net/YboaR.png