I think defined brows shape the face no matter the color of your hair. If you are going to get them tweezed you will have the shape already made so all that will be left to do is fill in the holes and maybe extend the tail if your hair is sparse there.
Use an angled shaped brush and a brow powder (or eyeshadow), i've tried a pencil before but powder looks more natural and is easier to blend. It's true using a black shadow or pencil is usually too harsh because it doesn't look natural on people. The way your eyebrows would look the most natural is by getting a color matching your eyebrows. Getting them darker to match your hair can make them look unnatural, which might be good for party makeup, but not for daily life. Getting a lighter color won't work either. You will see the color in the mirror at home, but under the sunlight it will be barely noticeable.