My S4 mini display suddenly changed!

One day, i was playing a game on my S4 mini and suddenly my phone's display colours changed. Now there are two strips on my screen- one is grey and the other is white!! it is showing negative colours(even when negative option in my phone is switched off)........I just want to ask that if it can repaired for free as it is in warranty or i have to pay for it assuming if my LCD is damaged? (My phone is working fine..i can answer call and i can see display also but its colour has been changed.)