Hi, I can help you with your question today.
The gray color is seen most often with stool retention and constipation.
I'm glad that you were given some dewormer in spite of the normal stool testing.
I would like to make sure that they received a specific dewormer called Albon (sulfadimethoxine) which treats for coccidia.
Coccidia is a parasite that I diagnose quite often in kittens that have blood in their stool.
Aside from that, I don't worry about color that much.
The most important thing is making sure that they are able to pass stool easily without straining.
If you see any straining in the box, I would start mixing some Miralax (PEG3350) into each meal.
For kittens, I would start with 1/8 teaspoon twice a day.
With regard to diet, I recommend sticking with the Science Diet kitten food.
You can use either dry or canned or a mixture of both.
This is preferable to the raw meat, as that can also contribute to GI disturbances.
Please let me know if you have further questions. I am happy to continue until I provide the service that you seek.