Inspired by this question on history.stackexchange about the etymology of "Belarus" = "White Russia"...
@SigueSigueBen writes in a comment:
There is a tradition of giving naming compass directions after colours in Turkic cultures. The best example is from the perspective of Anatolia, you have the Black Sea to the north, the Red Sea to the south, the White (Mediterranean) Sea to the west (the east is blue, by the way).
And the Wikipedia page for White Croatia writes:
The epithet "white" is related to the use of colors for cardinal directions among Eurasian people. It meant "Western Croats/Croatia", in comparison to lands where they lived before.
(The "lands where they lived before" would be Red Croatia, by the way.) That claim is simply a gloss by Wikipedia user Crovata of the equally unsourced claim previously added by an IP user:
[...] 'white' (cardinal direction north) would be somewhere at the upper Vistula/Slovakian Paradise, while 'black' Croatians would have lived in Lesser Carpathia [...]
What's missing in all this Internet game of telephone is some actual reference to original sources or peer-reviewed publications.
Is there any culture (Turkic or otherwise) in which cardinal directions are customarily associated with specific colors? Prove it.
UPDATE: Wikipedia's page on "Cardinal direction" has a whole section devoted to color associations in Turkic, Asiatic, and Native American cultures! But its sourcing still leaves a lot to be desired; most of the links are dead and/or point to personal webpages which themselves don't say where they got their information.