If the edges of his fins are tirning black and seem like theyre thinning out and falling off, then its probably Fin rot. Otherwise maybe its natural coloring? I've seen some bettas with natural black edges to their fins.
Take care of the ich first and maintain clean water until you are 20% sure the ich is gone. Then you can tackle the fin rot separately. I had first gotten my betta when he had fin rot and ich. I panicked and read up that that you can nuke fin rot surgically, I took him out of the water and applie some hydrogen peroxide to the edges of his tail. Boy was he mad at me. but the rot died and the tail started healing. Just a story :) i dont recommend you try it unless it is absolutely neccessary