Screenshot from the YouTube channel JBirdx665
I'm sure you found yourself trying to reflect the light from the sun with your phone or a watch in the face of someone just for fun (I know I did).
Well, this guy brought the trick to the next level: he noticed a rainbow reflection of the light passing through a window onto a brick wall. He then put his phone in the middle and managed to reflect one color after the other, lighting the whole room with bright and joyful colors...