This might be of interest to you. It is an answer by a pediatric opthalmologist to a woman whose baby has grey streaks in the white of his eyes.
It sounds to me that your baby's eyes have a little different pigmentation from normal, that is not entirely abnormal either. It could be either of two things. The layer under the sclera (the white part) is called the choroid, and is very darkly pigmented.....so if the sclera is slightly thinned that area can appear darker. Or it could be a normal variant pigmentation called ocular melanosis, where there is extra pigment in the sclera and this causes the sclera to appear slate grey. It is of no consequence.