MacBook Pro StainGate is a known issue on retina models where the anti-reflective coating is wearing off over time.
How to prevent stain gate on your macbook pro ?
Accordingly to Reddit , below are the following recommendation:
(1) Avoid Keyboard Covers
(2) Avoid Sweaty and Greasy Hands (Food) on keyboard and TrackPad
(3) Clean Keyboard and TrackPad regularly (Cleaning Wipes)
Esmond Service Centre Suggest :
(1) Clean Display Screen regularly with (MicroFibre Cloth) without any cleaning solution or use clean water