I think, what I understand you are describing is the beetle green sheen that can often look a bit, deep turquiosey/blue, is the green sheen that is being discussed. I see that on my birds too depending on the lighting. The sheens are a refraction of light on the feather, and how we see it, or at least that is my understanding of it from studying it. Hope others come by to give you their opinions as well. Have a great day!