The Great Red Spot is a persistent anticyclonic storm, 22° south of Jupiter's equator, but why is it reddish?

From Wikipedia:

It is not known exactly what causes the Great Red Spot's reddish color.

Are there updated data?

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    $\begingroup$ It should be noted that its color and size change in time. Right now the GRS is at its smallest in a very long time, and it's at its least reddish. Basically, it's the mild color of a coffee shop latte, more or less, difficult to see against the similar-colored background of the equatorial belts nearby. Observers using relatively small amateur telescopes have a bit of trouble seeing it even in good conditions - at an aperture of 150...200mm it's more visible at first as a dent in the nearby belts. This is in stark contrast with the deep red and large size of the GRS in previous decades. $\endgroup$ – Florin Andrei Dec 17 '14 at 23:44

It's red, because it's a 'sunburn'. The clouds in the red spot reach to higher altitudes than the surrounding and are more exposed to Solar UV radiation, which in turn changes the structure of some of the organic molecules etc. This is at least the explanation suggested by recent data from NASA's Cassini mission, see this 5 day old press release.

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    $\begingroup$ When I read "sunburn" I immediately thought you were crazy and needed a downvote. But it's serious. Neat. +1 $\endgroup$ – zibadawa timmy Nov 16 '14 at 18:36
  • $\begingroup$ wow, totally unexpected. great job! $\endgroup$ – rnrneverdies Nov 16 '14 at 20:48
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    $\begingroup$ @Deuterium I find it amazing that you ask this question just 3 days after this press release! What triggered the question? $\endgroup$ – Walter Nov 16 '14 at 21:20
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    $\begingroup$ @Walter I heard that years ago on a video, two days ago I was reading wikipedia and did not believe that is not known yet. I just hope that my chance on lottery was not spent here. $\endgroup$ – rnrneverdies Nov 16 '14 at 21:55
  • $\begingroup$ Really nice answer. Why did you delete the old one? $\endgroup$ – HDE 226868 Nov 17 '14 at 0:50

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