Facial fat grafting is generally very successful in reshaping the face, however results are somewhat technique dependent. The periorbital (under eye) area is particularly challenging because the skin is thin and riddled with fine veins, which can be injured during the procedure, releasing blood into the surrounding area. Additionally, the fat should ideally be grafted deep to the orbicularis oculi muscle to avoid visible irregularities. If you have failed conservative measures, gentle massage, warm compresses, camouflage make-up, discuss your concern with your PS. (S)/he may very well suggest treatment with Cutera XL's laser. A single treatment will allow dispersal of the pigment and resolution of your problem. Good luck.
Three months if a fairly reasonable time for most bruising to have resolved after fat transfer. If it is truly a bruise created by extravasation of blood products from grafting, you might want to consult your cosmetic surgeon or laser specialist for treatment with a pulsed dye laser which can help disperse and clear any residual tissue staining. I would less likely suspect that is was bruising if a hyaluronic filler was utilized as then you may be looking at an optical effect of the filler under thin skin. Hope this info was helpful.
this should resolve after 4-6 months. some of this depends on your skin type. olive or darker skin tends to stay bruised a little longer. warm compresses, massage and hydroquinone will help