Why do I still see a slight gray line at my gumline with an all-ceramic crown? (Photo)

Last week, I had a PFM crown replaced with all-ceramic and there's still a slight gray line at the gum margin. What is this from, and is there any way to get rid of it completely? I've been told that my whole gum area above the crown will always be discolored from the dark root showing through, but I don't understand why there's still a line. The entire crown has a slight gray "dingy" color to it. Is there any way to fix this after the crown has already been cemented in? Thank you in advance!