Take mine, for example:
they can look completely different depending on the light they are in. It is very hard to get an honest picture of their colors, 'cause their colors get in the way.
Ever try a sunshine shot? Doesn't work. The snake gives off a metallic shine like steel. A lit room shot with a flash? Forget it. Same shine off the scales.
Dappled sunlight or shade can make them look far darker than they are.
In fact, I am sometimes surprised at their color when I see them in different settings.
3-angle lighting works best for pictures, but it has to be pretty bright or they will look dark.
Also, they keep changing!
Mine are 4 years old, and look significantly different than they did last year. My male has very little grey left, and my female is only on the 'inside' of each coil.
I've come to think that color is just your perception at any given time, since these snakes' tones are so hard to pin down.
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...and I think to myself, "What a wonderful world."