to turn on safe mode press and hold your power off button then you will get power off , restart and emergency options, tap and hold on power off button later it asks to restart in safe mode, (you cant use any third party apps in safe mode) and check the problem is solved or its still there. to turn of safe mode simply restart your phone.
didnt work.... but i now found why that is happening. I have turned on bixby routine and set wifi to ON. So, if i turn OFF wifi when bixby routine is running my screen turns yellow. i dont know whether this an inbuilt feature or a bug.
