How can I put my Nintendo DS to its original colors?

If you can still make out the image, and it's not completely white, then it's likely not the screen or cable that is the problem. If you unscrew the battery cover you will see two small holes with what looks like Phillips screw heads. Turning these adjusts power to the screens, and improper power settings can make the screen appear too light or two dark. Adjust the screw (slowly!) until it displays properly.