Here is a mention of 'Green Croatia' meaning East Croatia.
Has anyone heard of Green Croatia before or where it is?

White Croatia, Red Croatia, Green Croatia
The Iranic origin of Croats is in fact the only way one can comprehend the traditional distinction existing between White Croatia, Red Croatia and Green Croatia:

    "After the Iranian fashion the ancient Croats ascribed a specific colour to each of the four cardinal points of the compass in the territory which they inhabited. The colour white designated the west, red the south, green the east, and black the north. (10: Saussure, Le Systeme 235-297; idem, L'origine des noms 23; Sakac, op. cit., 37-40) Hence White or West Croatia, Red or South Croatia and Green or East Croatia." (Mandic 1970, Ch.1)

from http://www.iranchamber.com/history/articles/common_origin_croats_serbs_jats.php

I can explain the colours :)

Colours to indicate a direction (West – White) etc is common for slavs and iranian peoples. It's a archaic trait that most scholars think comes from the common indo-european ancestors.