hazneliel That's true what keroberos said about the pallets in most cases, but contrast plays a big role as well. Generally speaking, objects farther from the camera are usually lighter than those in the foreground. I guess the science behind it is water/chemical particles in the air. Most artists will put a light colored gradient or fog on their backgrounds to give them a sense of distant.
I do actually like your color scheme, and if you don't really want to change it much, a simple way to separate the fore/backgrounds is to add a light haze to the background. It shouldn't obscure the background much if done right, so you can still show off all the hard work you did on the background and still make it easier to see what is going on in the foreground. Just make sure the haze is strong towards the bottom, otherwise it'll look strange.