Apparent Tone in Blackish Wingtips and Angle of Observation

It's no secret that a single photo of a gull at one point in time can be very misleading. This post is just another example of that. Specifically, note how the apparent shade of this bird's wingtips go from "sooty black" to nearly "jet black" depending on its angle to the observer:

 

Adult Thayer's/Kumlien's type. Lake County, IL. 21 November 2012.

 

This seems like a common problem with Thayer's/Kumlien's types and Glaucous-winged hybrids such as this individual:

 



 

Adult Glaucous-winged hybrid (GWGU x WEGU or GWGU x HERG). Gray's Harbor, WA. January, 2012.

Note the "apparent" change in lighting. This is due to a slight change in angle (by both the observer and the bird). In the top photo, I observed the bird on my right, slightly from the front. In the bottom photo, the bird is now slightly to my left, viewed from behind. There was no change in environmental conditions or camera settings in these two photographs.The overall effect on the wingtips is dramatic and likewise on the gray upperparts.  

 

Ultimately, I think it's safest to make an assessment of wingtip coloration in profile; preferably using a known species for side-by-side comparison.