Is your box color different than your natural color? Or are you just covering gray? If your color is not much different, you don't get a line of demarcation. That's because RC doesn't lift the natural haircolor so when it fades, you're not left with brassy hair. But it also does not lift your haircolor so you can't go lighter.

SF Bay Area, CA * "The Angel-Goddess-Guru of Haircoloring"
3b/c/a mix. medium texture, low porosity
My Motto: Strand Test! some hair pics
-- gone, but never forgotten.