Hidden colours in nature

Whilst walking to university, I came across a group of pigeons in the park searching for food. When I got a closer look at them, I observed a very unique contrast of shiny colours around their necks. It was quite a pleasant surprise as I had never paid much attention to pigeons before. Regretfully, I wasn't carrying my camera at that time so I've found a close up of a pigeon's head on Google for my blog. The glossy green, pale grey and a hint of lilac is indeed a very inspiring colour combination.

http://www.123rf.com/photo_6267336_head-of-domestic-pigeons.html