First off, an acne mark is the red, dark marks usually left from acne after it's been released and it's starting heal. Like after you pop a small pimple you have the dark red mark that takes a few weeks to completely fade off (sometimes it can take a long time, but in most cases at least it won't be permanent). On the other hand, acne scars are skin tissue that was damaged from the occurring acne and it usually has more of a skin texture issue. I've spent countless hours looking up things about the scars, marks, and redness left from taking accutane and from what I gathered acne marks are supposed to start fading because during the end of your treatment you should most likely be done with active acne and from then on out it's just healing. From the photo you posted I can tell that your discoloration and redness will significantly fade over the months. Good luck!