They are ramping down production for the molt and winter break, assuming you are in the northern hemisphere, you can get some weird eggs around that time.
Fairy, fart, wind, rooster eggs are usually from a tiny piece of tissue breaking loose from the reproductive tract, or an immature ova(yolk) and the body forms an egg around it. Color can be darker than 'normal' as the pigment coating released has to cover a much smaller area so is thicker. Can happen with any age layer, but more common with older layers.
I think it's explained in this excellent video, which is worth watching regardless: