Two things, your graphics (integrated or chipset) are going bad or your screen is going bad or your wires....what am I saying. How about more information, starting with what laptop you have and ending with...when it happens.
It's a toshiba satellite M35X-S149 and it is like this constantly. It really is more like dark yet faded rather than negative and some of the words are impossible to read. I recently did the left shift and alt key and print screen key procedure and it brightened the screen but a lot of the words are not readable making it impossible to use. I am not an inexperience user but I am not a computer novice or geek either. Any help will be appreciated.