Dart syntax highlighting is not highlighting dart code
As mentioned in the comments, you don't need the "Syntax highlighting only" extension if you have the Dart one, since the Dart one includes the same syntax highlighting.
Based on your screenshot, it seems like syntax highlighting is working fine - I can see multiple colours. I think the issue is likely the VS Code theme you're using. Dark (Visual Studio) only shows limited colours - try changing it to Dark+ and you should see more colours.
Dark
Dark+
To Change This Settings;
Setting Icon > Color Theme > Select Dark+ Configuration;
