We would have fifteen gods. Five monocolored gods that would be the major gods and ten two-colored gods that would serve as the minor gods. The colors would help give each god an identity that would tie the pantheon of gods to Magic... The ten minor gods will show up in Born of the Gods and Journey Into Nyx.
Yes, the Big Five aren't Therosian worshipers' only options - there will also be, to tie back into the themes of the past block, ten two-color gods. But who will they be, what sorts of characters will they be, and what will they represent? Let's try to figure that out for the allied-color ones first:
White-blue: This seems to be Ephara, god of scholarship and magic and patron of Meletis. The story goes that when the polis was ruled by an oppressive Archon named Agnomakhos, Ephara taught its inhabitants the secrets of spellcasting and enabled them to slay the tyrant and drive off his Leonin servants. Ephara basically resembles Athena, the goddess who protected Athens, the real-life city that Meletis is based on.
Blue-black: None of the known gods fits this color combination, really - but perhaps this will be the Hermes analogue. A messenger and spy for the other gods would be appropriate - being the lord of thieves and other malcontents fits that same purview as well as it does that of Hermes himself.
Black-red: Oh man, this is definitely Mogis. Let's see, the god of bloodlust who represents the anger and fear that arise from war, worshipped by Minotaurs, who are firmly established as Theros's main black-red tribe, and the dark and craven twin of the decidedly red-white Iroas? He even has a "red eye," proverbially - perhaps the other one is black.
Red-green: Okay, this one is complicated, and another issue for another time. Suffice it to say, we have evidence for precisely who the red and green god is, and to say any more would be giving away too much.
Green-white: Nearly as obvious a candidate for their color combo as Mogis is Karametra, god of agriculture. She's an associate and rival of Nylea, who, being monogreen, deeply resents civilizing influences. But after all, what is farming but the epitome of green-white philosophy: Imposition of order over nature, while still respecting it, in order to provide for a community.