I was reading up on my latest garden bird addition and I was surprised that the Indigo Bunting is in fact black! It turns out that "diffraction of light through their feathers makes them look blue. This explains why males can appear many shades from turquoise to black". I have to say it looked VERY blue to me ;-)
Personally I am happy about the optical illusion as they are a stunning blue. I turned the Indigo to black using Photoshop and it now looks more like a Junco - isn't color or rather our perception of color AMAZING!