What is this strange discoloration after Juvederm ? (photos)

Thanks for your question.  Without evaluating you in person it is difficult to tell exactly what the source of this pigment may be.  It could be bruising from the injection, although such a perfect line 1cm above the injection site makes it less likely.  To my eyes it looks like the same hyperpigmentation that I see all the time with melasma.  If it doesn't resolve in another week or two I would first suggest going back to your original injector to discuss.  If this doesn't help then I would see a board certified dermatologist who can help evaluate you for and treat you for hyperpigmentation.  Best of luck!