I'm not a graphics moderator but I did bear witness to discussion surrounding the rejection. Here's my thoughts on it.
Looking at the FG and BG, I think the best route you can take right now is to remove the FG entirely. Resubmit the file as Background/Layer 3 only. Doing this would allow you to use 2 palettes for the background instead of the 1 you're using right now, and allow you to have the background you submitted the first time. This one:
I think it looks fairly fine with the little anti-aliasing that's been done on the flowers and looks much better than having to use black outlines to fit everything on one palette row.
The reason I say to remove the Foreground entirely is tht I don't anticipate many people would end up using it over the BG. BGs can be used a little more universally, FGs can be very specific. This FG is incredibly specific, since it's just two giant flowers, and are likely graphics that would not fit many level types given their size and graphical style being very unique. So I believe you'd have a better chance at being accepted if you skip out on the FG entirely here.
Hopefully that makes sense. Submit just the BG/Layer 3 as shown in the screenshot from your first rejection and you'd probably be fine.