Why when i add a colored or in my case custom backround in cycles instead of the backround changng the color of my objects change?
In cycles, the Background BSDF is emitting rays and will affect the objects in the scene.
You have probably set your scene to transparent, which is why you can't see your background. Disable the Transparent property to see your background.
Using the Light Path node in the World material, it is possible to set a background, which doesn't influence the objects in the scene. This uses two background shaders. The first is visible to all objects in the scene, which is why it should be set to 0. The second is only visible to the camera. Plug your background setup into the second input of the mix node and connected the Is Camera Ray output to the Fac of the mix node.