The scars that Rowan found on Amber are not a result of her cutting herself, as a matter of fact she cant see her own markings, none of them can. The markings grow darker over time, and their color can be changed according to the person's personality, but it's different for each person. Also, the scar glows the color of the persons choosing. And just to wrap it up-
The scars are not from being harmed, the scars on the person are unseen to their owner, they change color per mood onmy known to the owner, grow darker over time, and glows when in in use to color the person chose. THERE YA GO, AN EXPLANATION.