Thanks so much for the comments, everyone.

I'd like to pretend I was being very clever with my colour choices, but it was really just basic colour theory. I had the deep blue sea colour, and I thought it was quite striking, but the typical land colours were just a bit meh next to it. So I brought up the colour wheel and spun it round to yellow and took it from there. I guess the moral is... if you're stuck figuring out a colour palette, go back to basics!