color part of short hair and make it hard

Hello i have an idea that is kind of hard to pull off and i really don't have an idea how i am going to do it. I am an african who have a natural black hair that if i let it grow for a long time i will get a fro. Anyway i want to color part of my hair brown and the other i want it to stay the natural color it is. Like for example do u know when someone gets old some of his hair is white and some is the natural color. I want my hair like that but i don't want part of it to be white but brown. What can i do, how can i do it and what materials can i use. Also how can i make my hair hard and make it look really nappy but at the same time neat. Please anybody give me some info and what i need to do.
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