There seems to be a rainbow color smudge underneath my screen

I noticed a weird rainbow color smudge that seems to be underneath my gamepad screen. Its barely noticable when the screen is on but when held at the right angle when its off it is clearly seen. I dont know how or why it got there. It also moves around as I touch the screen and follows my finger in a way, whrn I drage my finger across the smudge it expands and goes back to its original form after I release. Someone please tell me, is this a problem and how do I fix it if it is?