Syntax Highlighting in XF2 uses PrismJS, there are several themes for it available @ https://github.com/PrismJS/prism-themes
I'm a nub, but from what I can see, there is no simple way to import these into XF2 because of how PrismJS is implemented, not as simple as shown in the link above:
Since xenForo 2.0.1 release you can add additional language support on your forum. There was no way to do so before due to this bug.
This method of adding additional language was proposed by @Chris D.
In this example, I will be adding LaTeX support.
1. Downloading PrismJS components