Hmm... I see you dragged the icon from the custom mansions into some of the backgrounds. I see you wanted people to use this in the opening part or intro of the mansion, and you're looking at the mansion in the distance. If I where you, I'd go around the edges of the mansion icon and get rid of the white transparent stuff before you added it to the picture. It would look abit nicer. But it's fine anyways.
Notice: If I remember correctly, the backgrounds will tile if it's too small! A standard background should be at least 640x432. That's the size of the built-in backgrounds.
I tried that application you used. It's nice! It's a perfect coloring program. If you want to do more complex backgrounds like Joeb's dominator with that nice-3d stuff on the moon, you should get the nice, (now free) Bryce 5. There's a tread with the address to where you download it somewhere in the Art area.
I usually use gradients that have colors from a darker blue to a light blue for my backgrounds. I use Color It! 3.0 for that.
Wingy
P.S. Love that half water/half sky effect.