After more experimenting, it looks like the problem must be with my bitmap specifically. When I replaced my 48x2 with the "Yoshi" one from example 4, I didn't get the weird color as image background. When I did the reverse substituting my bitmap for the Yoshi one in example 4, I did still get the weird background color for my bitmap, but not for any of the others. I visually exaimed by converted bitmap and compared it visually to the working Yoshi one, but I couldn't find any problems. Any thoughts?
Mind you, this isn't vitally important, since I could always start from scratch with a new image if need be, since this one is more of a placeholder, but the mystery of it is bugging me. Attached is the compiled example 4 with my image substituted for the Yoshi one, and the problematic converted image itself.