I have had a great FUE result from a norwood 4/5 to having very nice hairline and density on my scalp. However, particularly under strong lighting, can see my scalp and some of the area on the middle of scalp. I've used over 5000 FUE grafts so I'd like to do SMP to cover up and 'thicken' the areas. My hair is dark brown, what will happen when my hair becomes grey over time if the SMP is dark brown underneath?