Press F5 to open a new window with your extension loaded.
Open File > Preferences > Color Themes and pick your color theme.
Open a file that has a language associated. The languages' configured grammar will tokenize the text and assign 'scopes' to the tokens. To examine these scopes, invoke the Inspect TM Scopes command from the Command Palette (Ctrl+Shift+P or Cmd+Shift+P on Mac) .
Adopt your theme to Visual Studio Code
The token colorization is done based on standard TextMate themes. Colors are matched against one or more scopes.
To learn more about scopes and how they're used, check out the color theme documentation.
Install extension
To start using your extension with Visual Studio Code copy it into the <user home>/.vscode/extensions folder and restart Code.