Around the drop there will initially be a higher reagent concentration in the test tube, resulting in localised pink areas once you get close. Once the latest drop gets properly stirred in by the speedstir, the pink disappears again. Only once the whole sample turns pink (more red, actually), and the shade of pink/red doesn't change when adding another drop and letting it stir in, you have reached the end point.
I tend to leave the speedstir's light off, especially with the FC test where the light makes slight shades of pink disappear. I also find the rotating shadow of the bean quite irritating. I have a little offcut of white melamine coated wood in my test box that I place behind the test tube, that gives me reproducible test conditions that make colour shade comparisons easier.
