Covering Gray

Hey, I was wondering, can you go to a salon and have them only dye your grays to match the rest of your hair? The problem is I have about 15 or so gray hairs in a streak in the middle of my head on the crown and I hate dying all of my hair (which I do at home because of the expense) just to cover up the small streak. I can't not dye it because I'm only 23 and I'm completely embarrassed to have any gray at all, but my doctor said that it's nothing to worry about and I think it may be hereditary since my grandmother had gone completely gray (or white, not positive) by the time she was like 32 or so. I remember her telling me when I was younger that she had to dye her hair because she was so fair skinned and she had to wear a white nurses uniform and she looked awfully washed out until she dyed it. Hopefully, I can stave off the grays longer than she did, but I still have that pesky streak and I think that plucking them out would be a bad idea. I don't want to have gray hair but I don't want to go bald or have a bald patch even more. I know that a salon can dye your hair exactly or acceptably close to your natural color, but I don't want to color all my hair the exact same color as it already is if I can avoid it. If it's possible to just have them dye one section of my head, do you think they'd charge the full price of getting your hair colored or would it be less expensive. If it would cost the same I'd just as soon get more for my money and get a full head of color. Sorry if this post is long but I'm so sick of dying my hair at home. I get Loreal Preference Light Ash Brown because the color on the box looks incredibly similar to my natural color, but when I dye my hair with it, the ends look good but the roots are too light. If I step up to the medium brown, my hair comes out looking near black (in my opinion, maybe it's just the shock of it, but it just comes out darker than I'd like). Any professional colorists or anyone knowlegable in hair coloring have any advice? Thanks in advance.

Thanks for the advice. I'm going to call around to a few local salons and see what they say. I just wanted to see if it was a completely ridiculous thing to do before I called and embarrassed myself.