Color patterns on the heads of birds are some of the most complex, and also some of the most important for identification. Understanding those patterns is significantly easier if you learn the five major groups of head feathers, since the contours of the feathers define most of the color patterns shown by birds.
In the photo below, you can see these feather groups and how they relate to the color patterns. To recognize these feather groups even on a species where they are all the same color, look for subtle “creases” where feather groups meet, and for the different planes of the head. For example, the feather group labeled D below is broad when viewed from the side but appears narrow (foreshortened) when viewed from the front.