Time for a new colorist?

She's added lowlights, but it always seems to fade to the blond.

I've been getting my hair done by the same person for about 10 years.  Naturally, I have medium brown, a little longer than shoulder-length hair.  My hairstylist used to just highlight my hair using foils, but when I started getting more gray, she started coloring my whole head a few shades lighter than my natural shade.  I go every month or so and just get my roots touched up.  I like the color of my roots, but as it grow out, it gets blonder and blonder.  It's actually mostly on the top layer.  Underneath, it's the color I want, a light-to-medium golden brown, but the top layer is yellow.  The ends on top are almost platinum.  Is this just the natural consequence of having your hair colored lighter than your natural shade, or is it something she's doing that someone else might do differently?  Help!!  I'm tired of having yellow hair.