"It is not known exactly what causes the Great Red Spot's reddish color. Hypotheses supported by laboratory experiments suppose that the color may be caused by chemical products created from the solar ultraviolet irradiation of ammonium hydrosulfide and the organic compound acetylene, which produces a reddish material – likely complex organic compounds called tholins. The high altitude of the compounds may also contribute to the coloring of the Great Red Spot."
What could be the possible reason that these specific compounds mentioned above are present only in the Great Red Spot?
Edit: Also is there a way to test as to whether the said compounds are from the interior or they are formed in the storm?