Error loading colour scheme in Sublime Text 3

You need to put the theme file inside Packages\Color Scheme - Default.sublime-package.

Open Color Scheme - Default.sublime-package with 7 zip (archive tool-you may use your favorite tool), and drag Monokai Gray.tmTheme into it. Then go to Sublime, and click Preferences -> Color Scheme and find Monokai Gray. When you choose the color scheme, it automatically updates the setting with this:

"color_scheme": "Packages/Color Scheme - Default/MonoKai Gray.tmTheme",

Note: I am using Sublime 3. I am not able to share my screen shot due to lack of reputation.

Sometimes, a couple of opened files ignores color schemes settings modifications, I had the same bug then ran this in the ST3 console :

[ v.settings().erase("color_scheme") for views in [ w.views() for w in sublime.windows() ] for v in views ]

This python code is pretty self explanatory.

With this, no need to close/re-open incriminated files for the bugs to go away.

Source

Menu > Sublime Text > Preferences > Settings - User> remove the line with `"color_scheme"`.

After saving the line was regenerated for me with a reference to a theme that actually exists.