A few pointers for when you do your eyebrows. First, please DO your eyebrows! Do not forget them! They're so important because they really frame your face and give you structure. A face without enhanced eyebrows makes it look like the eyes, nose and lips are just floating around, and we don't want that.
Second, your eyebrows do not need to be exactly the same! Actually, it would be better if they weren't mirror reflections of each other. Have you ever seen someone who drew in their eyebrows and obviously used a stencil to do the job? It looks just fake, and terrible! The more natural look is ideal, and nobody has eyebrows that are exactly the same. Remember, they're sisters, not twins.
Lastly, if you have black hair, you do not necessarily need to fill in your eyebrows with a black color. It largely depends on your skin tone. I have black hair and Asian skin, and my makeup artist suggested I not use black because it will look tacky against my NC30 skin tone.
Rather, he applied a dark brown color, and it looked wonderful! He explained that even though people have black hair, no one's hair is jet black. Exposure to sun lightens your hair to a certain extent, so it is better to go dark brown. Currently, I am using MAC's Mystery eye shadow to fill in my eyebrows. If you are interested, the picture is below, and this color is available at www.MacCosmetics.com for $14.50.
The opposite is true for people with blond hair, of course. If you have blond hair, you will want to go a few shades darker than your hair color to fill in your eyebrows. Experiment with different colors and see which looks the most natural and beautiful. I would probably start with the light browns. I hope this helps, and don't forget to do your eyebrows!