borders in excel 2007
 

I am working on a template in excel 2007, and somehow my cell borders are
changing from a plain thin black line to a shaded gray line. I've tried
selecting the cells and indicating borders around all the cells, and it will
turn the existing cells to gray. I've checked the line width (thin) and
color (black), but both on-screen and in print, the altered borders are gray.
Any ideas what I am doing wrong or how I can fix this?