What is this grey dark line on my face? I've had Restylane Refine placed in my marionette lines. (Photos)

Thank you for sharing your question and photograph.  It is difficult to see what may be taking place in your pictures as this could be a small bruise or a vein that is close to the skin surface.  I would discuss with your injectors' physician for the best advice. 

Thanks for your question. It's difficult to identify the cause to your problem by looking at these photos. I suggest a personal examination with a physician might be better for an appropriate diagnosis. Good luck, Dr. ALDO 

Hello, anikaxo 
Sorry to see you are not entirely content with your soft tissue filler. I cannot tell what the line you are referring to is from, I also agree with the other answers, it can very well be a small bruise from an angry vein or vessel in the area (there are a few vessels that encircle your lips) or if it just a matter of light reflecting through the thin skin and creating a blue hue. 
a bruise will settle and improve with time and patience, but the Tyndall effect only gets better by either allowing the body to remove the filler over time or by assisting the removal by applying some enzyme in the area (Sometimes this excess filler sits higher on the skin because it was injected superficially (the most common reason is while you are pulling out of the tissue and injecting while you pull the needle out) 
take some new photos, in full lighting so that no shadow is cast on your face, it also helps if you have direct views. not just an oblique or profile view. 
hope this helps!