Another interpretation: the waters, what are these waters? Some of them are red, some green, some white, some black. So too are the heavens: sometimes red, sometimes green, sometimes white, sometimes black.
Why the Sky Shifts Through Many Colors Like Water
Yalkut Shimoni on Torah 3:7
דָּבָר אַחֵר, הַמַּיִם מַה הַמַּיִם הַלָּלוּ, מֵהֶן אֲדֻמִּין, מֵהֶן יְרֻקִּין, מֵהֶן לְבָנִים, מֵהֶן שְׁחוֹרִים, כַּךְ הֵם שָׁמַיִם, פְּעָמִים אֲדֻמִּים, פְּעָמִים יְרֻקִּין, פְּעָמִים לְבָנִים פְּעָמִים שְׁחוֹרִים.