Shiva Purana
उकारमुत्तरे रक्तं मकारं पश्चिमे ततः॥ अकारं पीतमेवं तु कृत्वा वर्णचतुष्टयम्॥ २७॥
Ukara in the north and red Makara in the west. The yellow letter A is thus made into four colours.
english translation
ukAramuttare raktaM makAraM pazcime tataH॥ akAraM pItamevaM tu kRtvA varNacatuSTayam॥ 27॥
hk transliteration by Sanscript