Just to throw this out there, the BG color for .noticebar on the page MediaWiki:Common.css should be #F9F9F9 not #efe. If you look at it on a screen with a massive resolution the green shows, which looks weird.
Re: Jelloland - banners and icons
Well, I see you haven't dealt with HQ files just yet, so here goes;
Icon or Banner
Size: Eh, large.
Image(s): Have a nice day!
Text: Pika no like text. (And don't bother adding that 'cause that isn't text I want)
Additional instructions: You don't have to...