Is this colour change residual ink, ghosting or hyperpigmentation and what is best to treat it? (photo)

Thanks for your question and posting a picture.  That is how it is supposed to look.  Your body is chewing up the ink.  Colors will change has it fades.  It looks like you are getting an excellent result after just a few treatments.  If you were experiencing ghosting, the underlying skin would be very pale.  I don't see any evidence of that.  After 4 Pico treatments, we suggest you wait 4-6 months between treatments and let your body's immune system do the work.  Best of luck, but it looks great.

your tattoo is fading nicely, you just need more treatments. 4 sessions is not that many. The picosure laser cuts the number of needed sessions by half. it is the best laser for tattoo removal (and for laser facials).david berman md

Hi Dear
You might need more treatment, Tattoo removal takes many treatments, The best Laser Tattoo removal at this time is Picosecond Laser Tattoo Removal