ELI5: Why do tinted windows almost look like a grid when you wear sunglasses?

a couple of weekends ago I was driving somewhere and we were stopped in traffic and I mentioned to my passenger that was an odd choice to make painting the tailgate of the truck that was in front of the car I was behind.

My passenger asked what I meant, as it was the same color as the rest of the truck.

I realized I was looking through the tinted rear window of the car in front of me, and the tailgate just looked like it was a really dull brown color with rainbow accents.

I started laughing, pulled my sunglasses up and sure enough the tailgate was completely normal and uniform with the rest of the truck; my passenger couldn't figure out why I was laughing and I handed them my sunglasses and they said "Ohhhhhhh"

/r/explainlikeimfive Thread Parent