So before I had actually done the backgrounds I had to finish my animation on the characters. That actually proved less difficult than I had originally thought and I was very happy with how they turned out. I basically created 4 amorphous characters that would come in after the live action characters had been pulled inside the letter.
The designs came from my earlier class of Ideation and Preproduction which I took as a Junior. I had drawn a bunch of different designs which I posted earlier in my blog and I took those designs to create my characters. I wanted them all to be very different from one another and kind of be somewhat relatable to the real life characters they were portraying. I got some great feedback on the movements I came up with and didn't really mess with their movements after that. Once I had some cycles of them playing their instruments, it was fairly straightforward to put them into their respective scenes.
The way I chose to color them really came up kind of randomly because one night as I was working on some other animation I came up with coloring them in with a colored outline and filling them in with black. That way I could take the Flash sequence and bring it into After Effects and apply some glow and scatter effects to make them stand out. I later applied that to how the characters would be pulled into the letter and it ended up having nice continuity.
Here it is: