This is such a difficult problem, and scars like this usually bring back old memories of the painful injury which can make it a constant reminder. For a treatment to bring back pigment, there needs to be a remnant of follicles in the scarred area--the follicle is where there would still be melanocytes, or cells capable of producing pigment.
If many types of lasers haven't helped, then it is unfortunately unlikely that micro-needling would help, as there probably aren't any follicles left in the scarred area. One could consider medical type tattooing, to try to match the surrounding skin, although that is hard to match. Trying to protect from sun/bleach the surrounding skin may help a bit. This is very hard and sometimes just not responsive to treatment.
