One form of body art that can be subtle and totally natural or highly-fantastical is the coloring and shaping of the eyebrow. For the most part, due to the placement on the face and direct interaction with emotional expression, most people go for changes that are gentle and natural looking but that isn't always the case.
Eyebrows are hair that grow along the upper edge of the eye socket, lying on top of some very mobile and expression facial muscles. Lowered when the eyes squint, they help convey anger and intensity. Raised when the forehead goes up and the eyes widen, they help communicate surprise or shock. Any cosmetic changes to the eyebrow can have the effect of signaling one predominant emotion or expression if done improperly.
Most women (and men) who choose to do something to their eyebrows simply remove some of the hair to reshape the overall outline of the brows. This process is done either via a variety of techniques that pluck out hairs or shave them off. This can help make the brows lighter in appearance and more mobile and expressive. Some people chose to do away with their eyebrows altogether which can have a strange effect on the appearance of the face as humans are used to this element of eye framing and communication.
The next most common process is filling in the brows for people who either don't have much in the way of eyebrow hair, or whose eyebrows are so light in color that they are harder to see. Most often this is done with a eye pencil, where the brow color is matched and the shape is gently augmented with coloring and shading. But some people like to artistically style their brows, making them much bolder on purpose. While a common technique for stage theatrics, it's not as common for street makeup.
Some people choose to remove their natural eyebrows and have tattoos for replacements. These options can include copying the shape and style of a natural brow or it can be so that something entirely stylized is the result. Tribal swirls, rows of dots and small designs have all been tattooed where eyebrows once were. That method requires the most care as it is permanent and anything that is too heavy or placed badly can result in a singular emotional expression. For example, placed too low and a tattooed eyebrow can result in someone looking like they are always scowling or glaring at others. Too high and you might find yourself wearing a permanent look of surprise.