A bit of general info on parameter names hints can be found in this official introduction blog post: https://blog.jetbrains.com/phpstorm/2017/03/new-in-phpstorm-2017-1-parameter-hints/
Now back to the actual question:
NOTE: It’s all working since 2017.1 version
Either right click on such parameter and choose appropriate action from the menu
or go via Settings/Preferences directly:
Settings/Preferences | Editor | Appearance --> Show parameter names hints
In latest 2019.3 version this option is now located at Settings/Preferences | Editor | Inlay Hints
where you can configure that on per supported language basis:
If you wish to customize colors used to display such hints (especially viable for custom color schemes that use dark background colors) then please do it at
Settings/Preferences
Editor | Colors & Fonts | Language Defaults
Inline parameter hints
node.