Question about elemental chests color selection

Just want to check to be sure:
The elemental chests I got so far always had a different color until I got to a red one.
Now the third time in a row I have a red chest.
Isn’t the color of the chest supposed to change?
Is it random?
Or should it actually “rotate” through colors?
Am I just unlucky to always get a red one or is there some problem?

It’s random. I almost get 80% dark or red…