As GodReborn explained, that's all you really have to do to get it on your Wii U permanently.
Thanks, honestly purple wasn't the first dark theme I intended to do, as I planned on going blue or red first, but since I started working off my initial theme, there were a lot of purple elements already in there so I kinda just ended up adapting to that as the first dark theme. And speaking of which, I believe I can consider the purple variation done. I was hoping to drop multiple dark themes at once, but these really are time consuming. I am going to do more, but I think today, I will officially drop the purple dark theme as I feel it's ready to be shared.
I want to note a few things first: screenshots don't always do the actual picture justice. In my tinkering, it became clear that my TV outputs color a little differently than how the GamePad did, as such I had to kinda find some happy mediums, because things that look purple on the GamePad sometimes come out a bit pink on the TV, and so if I go with a darker blue/indigo, it'll show up as purple on the TV, but look a bit dark blue on the GamePad. Not a big deal by any means, but I had to really work hard to find colors that looked purply enough on both displays. The screenshots you see are more representative of how they look on the GamePad since I captured them directly with a capture device.
On top of that, there are little things I don't quite know in all of this, like the corner selectors around an icon still maintain some blue, as does the loading circle when you see it, despite there still being purple elements in there. Obviously, blue works well with purple, but once I get to more themes, this might look a little strange like if I do a dark theme with yellow highlights. But I'll cross that bridge when I get there. For now, check out the final version of the purple theme and download it if you like.
Download Here