Doctorates are made of such topics...
Evolutionary Photonics of Avian Non-iridescent Structural Color
As the American dude would ask me, “which part of that don’t you understand?” And the answer would be, “all of it!”
That’s the topic chosen by a student of Yale….figures….
That’s about as far away as one can get from my poor “Oh! Look at the Ashy Prinia”!