What is this strange discoloration after Juvederm ? (photos)

From your photos it looks more like melasma than a consequence of the filler injection. Melasma can darken quickly if you had some unprotected sun exposure after the procedure.

This does not resemble the Tyndall effect. It looks as though it's just a slight bruise and will clear up without intervention, if in fact this was not present before the injection. If it was present before, then it represents hyperpigmentation.

As stated in previous question about this same problem, it is a bruise that will gradually get better. Arnica might help it resolve faster. Cannulas help decrease the risk of bruising.

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!