My guess is that Geany does not monitor the theme file and one needs to reload it somehow.
That's true. But `filetypes.common` is monitored and if you edited line 10 as suggested, you would get the change immediately.
BTW, as for the two gist links you posted (L10 and L111): They are identical, i.e. while the gist link is different, the text in the two is the same (I used a compare tool to make sure that I don't miss any difference).
They are identical - they are yours ;-)
I just emphasized the line number which you should edit - you edited line number 111 which corresponds to the default theme and this won't work for the theme you use. Instead, you should have edited line 10.