I use Notepad++ to create and edit QuickBMS scripts (makes indentation easier). However today I looked into making custom syntax colouring and such for it, and it wasn't too hard. Basically I just made it colour various commands and data types, as well as comments and strings. It makes script a bit more readable and less bland to look at. It also allows you to collapse if statements and loops.
I've attached an XML file with the language definition. To use it, in Notepad++ go to Language -> Define your language, then click Import and select the XML file. It should automatically detect .bms files to be displayed using that definition.
Hopefully this is helpful for some people, I definitely think it makes scripts easier to read