Did you use remove light pollution, calibrate background and calibrate star color? The last step, currently will make the ratio of red and blue stars equal, but white stars become greenish. I think I can see this in your image? There is a bit of Green cast to the globular cluster. You can easily correct this with the selective color tool:
select green and add opposite of green -> magenta, 75% . You can do it twice are more by clicking apply and continu. After 2 or 3 times, the green cast will be gone completely ;-)