In NetBeans it may happen with you that you are selecting a theme but its not showing any effect in your file.
To select a theme you need to go – Tools => Options => Miscellaneous => Fonts & colors
Here you can see a drop down named Profile .
Now if your theme is not actually highlighting keyword , comment , link , script in different colors then you need to check the “Language” drop down .
If your selected files programming language is not present in the list then this can be the reason of not highlighting.
So lets go to the Tools (Menu) -> Plugins (Menu) -> Available plugin (Tab)
If no plugin is showing in your tab then you need to go to the Settings tab in the same dialog.