(Votes for the background of the Ocean, with the main background colour being the bottom-most colour of the ocean background.) So now all we have to do is wait for Ngo's go-ahead? Cool.
That was my point. Anyone can do it, but it's a little hard to really do without a URL to work with. Recommended sizes are 1920px wide by anywhere from 1080px to 2160px high.
Will it be okay if I have, say, two different pics and you trim and fit them with the space in the middle? I'm going with Ex's idea of hallow and corruption.