Major mode for editing neon files: http://ne-on.org/
The mode provides some extra syntax highlighting on top of conf-colon-mode, specifically for the @entities and %parameters%, ::methodCalls and $variable-style setup.
All the features should be demonstrated on the following screenshots (the colors of various elements use font-lock faces so they will look compatible with your theme).
If you use composer autoloading in your project you can use a "Jump to definition" functionality bound by default to M-'. With the point on the class definition this will use the autoloader to find the definition file and visit it. Use pop-global-mark to get back to the neon file.