I have gall stones. When I'm having a really painful episode I start to see black why is that?

The severe pain. Severe pain from any source can cause one to feel faint or completely pass out (syncope). The symptom your having is like a blackout (pun intended). More important is that u r having recurrent episodes of severe pain. The main question is r these truly due to gall bladder disease, has it been diagnosed properly. If yes, get it removed by competent general surgeon and have good preop med clearance.
GALL STONES. When you have gall stones and you get an attack then it is very painful and most patients describe it differently.You need to discuus your pain and seing black with your doctor and, may be you need to have your gall bladder removed or ercp.Talk to your md or gastroenterologist.