From Hubble in narrowband red, mediumband green and blue filters. I did not enhance the saturation for this image; the filter choices manage to separate the colors on their own with little processing effort required.
It is important to note that no one has seen a clear image of Neptune directly without the aid of a camera and various processing techniques. With that in mind, I have tried to modify my Hubble processing to match more closely with the Voyager 2 data. I have noted that the blue channel must be more emphasized, and the green channel less emphasized to approach what others have reported seeing regarding the human-perceived color of the planet. I have relied on the advice of H. B. Hammel and Björn Jónsson from short Twitter exchanges.
Here and
here.
I would guess that this is more saturated than Neptune may appear to a human eye, but it's hard for me to say. Based on this and the Voyager 2 data, I am intrigued by the possibility that the pinkish limb may be visible to a human eye, if a human was ever to travel there and bear intimate witness to such an elusive majesty.
The high clouds in the northern hemisphere have been evolving for the past few years. Previously, bright cloud formations have been noted nearer to the equator. They are large enough and bright enough that amateur astronomers have also been recording them and
collaborating with pros. (Hat tip Björn Jónsson)
The easiest way to see the changes documented that I know if is via the OPAL website, by loading the various Neptune tables.
archive.stsci.edu/prepds/opal/
Red: WFC3/UVIS F657N
Green: WFC3/UVIS F547M
Blue: WFC3/UVIS F467M
North is up.
