You will need a solid image stamp, two coordinating ink colors (one light, one dark) and of course...cardstock to stamp it on! Ink up your stamp in the lighter color. Then switch to the darker color and instead of pressing it down on the stamp pad only press the outside edge of the stamp to the ink. You'll have to "rock and roll" the stamp around to get all the edges covered. The more you do, the more extra color you grab. It creates a bit of a gradient effect and depending on the stamp image you pick, it can create a darker border.
I've been using this technique for years and I love it! So Friday when my brother said "do you have a card I can have for the wedding tomorrow?" I said "Sure!" cause I knew this technique would give me a great looking card fast!
I used Stampin' Up!'s "Cottage Garden" and "God's Blessings" stamp sets in Bashful Blue and Pacific Point.