I can tell that you did consume a lot of berries !
I don't think they do any harm to your body but
infact are good antioxidants
and will help to boost
your immune system. So, don't worry.
As to how long the fiber particles take to clear out
of your system, depends on the strength of your
contractions. Some people have a slower
transit ,while others may have rapid transit time.
If you are still seeing some specks of black or dark
mixed in your stool, I would not worry.
It might take a whole week before your stool turns back to normal.
By the way, spinach in excess can change the color of your stool also.
I wish you well.