Wow, this is weird! I'm making a wall of Mio on this background taken from a screen cap from the ending credits!! I totally understand your pain with the background, it's a total pain in the backside. I'm having issues with it too. I've resorted to painting it roughly with a brush dabbing in all the colours and then when I'm done I'm going to apply a blur too it. I'm hoping it'll give a similar effect. Here's what I mean... It still needs a lot of work so excuse the cruddy-ness!
I think you did a great job with it though seeing as it's so nightmare-ish. Ritsu looks cute, although I think the lines are a bit too jaggedy. Aside from that though you did a good job! I hope my ramblings help in some way :3
Xx
Edit: Thanks Staniol, it's changed. Whoopsie!