slice_69, Sadly text background colours are hard coded into the firmware and can not be changed or at least I have not heard of anyone managing to change them. As not all firmware use the same layout when building a theme you generally have to design it around these permanent items.
Can you upload the firmware to
www.uploaded.to and leave a link.
Also where did you get the 9.0.48 for your player from? If possible can you upload it to site as many members are needing recovery firmware for their dead players.