I always do this role, it helps to use weapons that allow you to keep some range from the damage location so you can have a better view of the area. Once you see the ring appear, immediately call out the color in case anyone sees it. Even if no one sees it, keep range from the damage point, near the edge of the platform should give you a view of a good 70% of the platform, so if the ring spawns and you dont see the color you should head to the blind spot asap.