Depends on where they are coming in love.
In the eyebrows they are much thicker than the other eyebrow hair, tending to grow longer as well. Plucking works best for the short term. If you start getting em in clumps, then trimming is the best. As a woman you have makeup to hide them better, thus trimmin to match the length of the rest of the hair with the application of eyebrow pencil to even the color.
On the head? depends on your do. If your do is long it will tend to show a grey hair much better than a short do. Keeping the grey hairs short will let them hide in the rest of the hair. If your do is short, white/grey hairs are not as noticeable. One of the reasons why women tend to start going for shorter hair styles the more mature they get is to hide the grey/white hair without resorting to coloring.
If you have dark hair to begin with white or grey hair will show much easier, you may want to just pluck until you decide to go with coloring. Even short light hair will show up if the contrast is great. Those with light hair will find that white/grey hair only shows up when the light hits it just so.
As for Coloring, there are several products on the market which are designed to blend the grey/white hairs with the natural color of ones hair. These are great for intermediate graying folk. These are cheap, easy to apply and work just as good as a professional coloring. Not just for the Ladies, Gentlemen - on that same note there are special waxes for facial hair, and even coloring for facial hair.
These work best with around 10% of your head is grey. Beyond that you should start looking at dying all of your hair a lighter shade. Dark hair tends to make a white person look older than they really are (Thus the fascination for blonds blonds have the look of youth).
There are several kinds of coloring one can get from a stylist:
Frosting, which introduces more grey/white hair but in a nice way.
Highlighting, which introduces lighter shades of your natural color.
Full color which is most often used to change the color of all of ones hair.
Or a combination off all of the above.
All of these work well, unless you are going for the cool look of Rouge (
http://www.fcph.us/wallpaper/images/X-Men_-_Rouge.jpg) She has a streak of pure white hair on her head.
I do not advocate plucking of hair on ones head. The scalp is sensitive and plucking means you are ripping the hair out by the root leaving a hole where debris and germs can get in and form an infection. Cutting or trimming the individual hairs is best when possible.
Your stylist can cut your hair and blend it in a manner which hides the white/grey hairs. That alternative may work best for you.
Cheers
David