The issue of a player quickly going from blue to black in a category has been discussed at length on the forums. It just means the guy had just over 20 points to gain from his initial rating, so it was listed as blue, and then after a small gain he had less than 20 points left so it goes to black. Its always frustrating to see, but it has a perfectly logical explanation.
That is one area that scouting trips can be nice because you can tell if a rating is low-high or high-high, but its still far more efficient to use FSS for the most part. If you are trying to decide between two players then the scouting trip becomes valuable to differentiate between the two if one has more high-highs.