Changing refresh rate from 60 to 90 will do nothing if you're shooting in 25/50fps. The refresh rate needs to be divisible by the frame rate. You can alleviate it by changing the shutter speed, but 1/60 or 1/30 are your only real options if you are shooting at 30fps.
The discolouration on the screen is thanks to the polarising filter on the phone. Sometimes it's because there's a removable screen protector, which you should take off.
Personally, I'd get a green background and track/overlay whatever it is you're looking to shoot. The screen will never look that great if you're trying to showcase something on there.