A rule of thumb is that the color of your eyebrows should be the same color as the darkest part of your hair. However, there are plenty of blondes out there with naturally black eyebrows so you just have to do some testing to see what color looks best on you. Be careful not to choose a color that looks to sharp against your face (unless you're specifically looking for that kind of effect).
As stated in the eyebrow bleaching section bleached eyebrows will very often turn black when applying any eyebrow coloring product to them. It's almost scary, sometimes it only takes about 20 seconds before they're completely black! This is because bleached hair becomes very receptive to any color. So, if you've bleached your eyebrows you might want to color them with a regular eyebrow pencil. Even some firm eyeliners will work. That way you can get the exact color of your choice.
Permanent eyebrow coloring
Permanent eyebrow coloring lasts for about four weeks so you don't have to worry about filling in your eyebrows every day. There are plenty of products out there for eyebrow coloring, most of which are really easy to use. Typically manufacturers sell black, brown and red eyebrow coloring and there are often different shades of brown. If you're choosing between two shades, unsure of which one to pick, choose the darkest one. Don't use any hair color products on your eyebrows as they can be harmful to the eyes.
Tips on applying eyebrow color:
Use a make-up remover to remove make-up from your eyebrows. Then clean your eyebrows from oil and fat.
Apply the color paste on your eyebrows. You will sometimes have to mix it with a developer cream - check the product manual for details on your specific product. Make sure you cover the entire eyebrow, even the hair underneath the upper hair. Be careful not to get any color paste in your eyes.
At the end of the application time (see bottle/tube for instructions), remove the paste with a dry cotton ball. Then use a moist cotton ball to remove any excess and finally use a make-up remover.
I would advice against tattooing of the eyebrows. In this case permanent means something different than above - it means forever. What if you want to change the shape of your eyebrows at some point? Also, I find it a bit risky - how do you know you can trust your tattooist to make exactly the kind of eyebrows you want for the rest of your life? With permanent eyebrow coloring you don't have to bother about your eyebrows for several weeks. How bad can it be, spending about 15 minutes a month on coloring your eyebrows (that includes waiting time)? You still have to shave the real ones off if you have a tattoo. And most importantly, remember that the eyebrows have a function! That is to prevent sweat and dirt from entering your eyes. Alopecia patients (who don't have eyebrows) have explained that it makes a big difference not having actual eyebrows.