For now this is a replacement for the powershellDef.js file that defines the syntax colorization for PowerShell tokens like variables, strings, etc. There is also a file - powershell.json - that contains many useful PowerShell snippets.
To get the improved variable syntax colorization, drop the vs.language.powershell into your VS Code install dir:
C:\Program Files (x86)\Microsoft VS Code\resources\app\plugins\vs.language.powershell\out
It wouldn't hurt to make a backup of the original powershellDef.js file. Of course, any VS Code update is likely to replace this customized version of the file. So you might need to put this version of the file back after an update. That said, I am working with the VS Code team to get them to take these changes and put them into VS Code.
The snippets file - powershell.json - can be installed by copying it to the following folder:
$env:UserProfile\AppData\Roaming\Code\User\snippets
Let me know if you find any issues.