Suggest Hardness And Blackness Of Skin Around A Healed Laceration

My son had a laceration on his knee on May 21st. Eight stiches were removed on June 1st and it has been healing well. I think that it is just a scab but the area appears kind of hard and blackish. Is that normal? It is irritating him a bit but it is not oozing. It is quite dry and a bit red around the blackish part. the blackish part is hard