I think that's a change in the theme of Notepad++, rather than having something to do with the highlighter itself. The initial version on the wiki was light as well.
Also, once you've installed the highlighter, you can customise its colour scheme in Notepad++ easily with the User Defined Language dialogue.
Cipscis
Well, you actually have two different sections for notepad++ as far as highlighting goes, there is a style configuration thing you can use to choose between several different presets which cover the languages built in; Then you have the user-defined one.
You can change the preset to a darker color, and it will mix with the user-defined colors, but the colors in the one released are designed for a light-colored theme so you will have to manually fix them.
Was hoping to avoid having to manually fix it, that's all. It's not a big deal if I have to, though.