I did a fast edit of what IMO would look better.
The tiles look better now, but I think it's better to keep the BG as a BG, with a softer palette (so I cropped the tiles on your last edit and pasted them on the bg you had before)
The oulines on your characters are too light now, I meant it more like if would look better if it weren't that dark, but they need to be dark enough to highlight the sprites.
I put a dark blue, but not as dark as the one you had (and randomly changed the colors of one character, so it could work as an enemy or something).
Looking good though. Can't wait to see what it ends up like.