MonoDevelop 5.9 adding syntax highlighting .json file does nothing (WINDOWS, UNITY 5.3.1p1)

I updated to Unity 5.3.1p1 and within that came MonoDevelop 5.9.

Before that, I was using Unity 5.2 and MonoDevelop version 4.something. And before updating, I used Custom Dark theme from an awesome guy named Sebastian League (check out his videos!). It was added by ‘Tools → Options → Text Editor → Syntax Highlighting’ and then pressing ‘Add’ and selecting the right file.

But if I do it now, after ‘Add’ and ‘Open’, nothing happens. It goes back to ‘Syntax Highlighting’ window, but no theme added.

(.GIF down here)

I tested with duplicating other themes and tried different ways of doing it, but nothing.
Any help appreciated, thanks!

I have the same problem .But today I got around it.
My MonoDevelop 5.9.6 with Unity 5.3.

Reason for import but nothing Happened:

  Mono is very sensitive and strict for the format of the *.json file(more loose for *.vssettings file in my experience).
  E.g .`{ **!!--space or Tab here--!!** "name":"Background(Read Only)", "color":"#D9D5C3" },Maybe have many points that matter ,So you'd better to compare you json with default ones (you can export one for comparing by BeyondCompare or other tool you perfer).

Btw,Good place to download the excellent styles for free is

Any I prefer there ones: