Don't worry if nobody replies on your thread. I know it was said before, but majority of users only post when something you made has some problems or looks simply astounding. Neither of these things have happened yet. The reasons why I'm posting this are explanation on why nobody posts and 5-Castle.
Speaking of the last level, it's pretty nice that rooms have different colors and the boss fight has stones in three different colors and the background in a different colors.
I think that you should make the backgrounds in other sublevels slightly darker, so they don't blend too much with those stones.
Never mind, they're looking okay. Keep up the good work!