It isn't easy to recolor hair and just select those fine wisps without coloring the shirt.
You may at some point need to add hair addiitions to a selection of a model. Sometimes I "cheat."
My suggestion for that kind of technique:
Download some brushes to create hair strands. (deviant arts has some good ones)
Stamp/clone over the ones currently there so that it looks realistically like the t-shirt. Now make a new layer above. Pick the color you already used on the hair. You can select it from the paintbrush mode, clicking on the top color square in the tools box, ad click on the color you want. Then you can pick in the color choice window to pick the correct color.
Now on that new layer, use the hair strand brushes to add soft, light colored hair over the tee. They will meet the other hair kind of bluntly. You can fix that with a medium soft or soft brush. Create a mask on the same layer, use the top color - black - slowly at low opacity for the brush, blend it into the hair.
If the color is still slightly off what you want, add a layer adjustment>hue/saturation and make the color the shade and hue you desire.
Both methods described above by chris and sam work quite well for what you need to do. I use the method described above mostly if the selection I made of a model, created a cut out that didn't show all the wispy hairs. Then make a layer below using the same method I described. You may have to pick the color up more than once from different parts of the hair to make it blend with highlights and shadows. Takes a bit of experimenting, but once you get the technique down, it works very well.
So, keep this method to try if you ever need to deal with this for a client or for yourself.