This game seems fun, But I have to agree, the character and the collectible things are hard to distinguish from the background. Normally what I do is give Important things a black outline and give background elements no outline or outline of a somewhat light colour. You will also need to make sure that the player sprite will stand out from the background to help the player to make decisions more quickly.
I think the concept is interesting and I don't mind the poop theme as long as you don't make it too disgusting.