Aww shit, I think it's fair to say we can now have themes on the Wii U:
You'll note I changed a few more things than OP, including hte color of the buttons floating in the background as well, as the USB drive color in the bottom left, the color for the page your screen is on as well as the color of the pages your screen isn't on. Plus I changed the color of the 4 corners selecting the current game. Fun fact, this was just supposed to be pink, but this color actually kinda breathes and moves across the corners giving a mix of pink, purple and blue for the 4 corners, I think it works for the theme I've put together.
here's another image to illustrate the point, note how instead of the top right corner being the most pink of the highlighted app, it's now the bottom right that is most pink
Of further note, the page indicator colors and the color of the 4 corners around the highlighted title actually had to be altered within the separate file Men.pack as opposed to Men2.pack for most other things. And there is definitely more content within both files that can be altered, pretty sure just about anything you see on this page can be discovered and I intend to look more into it to further refine the theme I'm working on here.
It all pairs nicely with the custom wara wara plaza files I have.
Right now, this is all loading from SDCafiine. If I'm feeling daring later I may try and go permanent and add it in via FTPiiU. I know that sounds risky, but I've permanently alterred the Wara Wara Plaza, and not just in SDCafiine, and that works without a problem. But before I do that, I wanna finalize this theme, I know I can easily change the pattern of the floor that the Mii's stand on, and that is something I may want to look into. Plus there are other aspects I'd like to change, mostly things that glow blue, like the magnification of the Wara Wara Plaza in the bottom left corner of the plaza screen or the blue highlight over the game you're currently selecting; ideally I'd like to change those to be pink or purple to really tie the theme together, but I'm having trouble finding what part of the file I need to alter for those things. I'll look more at this tomorrow. But so far I am loving this information overall.