Hey bella123, it depends on how much H202 you use in your bath. I use a very strong solution most of the time, so I don't put my hair in it. I do think it's good for the scalp. I just use less ingredients if I want to put my scalp in the solution.
If you have dark hair, you may see some highlighting similar to spending too much time in the pool in the summertime. So you may have orange or red highlights if the solution is strong. Of course this is after taking many baths.
If blonde and not color treated, you may just become slightly blonder.
I would not recommend a strong solution on color treated or dark hair.