The pictures don't do justice, but check out my thread in Picture Post: first time refinish/upgrade. I refinished my whole stock with 1 coat ebony stain and 3 coats satin rattle can poly.

If you're only wanting to the fore end cap like Hotolds mentioned, ignore my post. I have no clue how to do it. Best guess would be to use a latex type paint to paint a thin line to separate the stains to achieve the desired affect.

There's a thread directly related to this, can't remember the title though.