How did you choose to configure the colors?
I'm trying to fit the qualities of individual characters with the qualities of magic colors and combinations. Tyrion is absolutely blue, as knowledge, manipulation, and control are qualities of blue magic. Cersei, however, is red/black—impulse, passion, and destruction from red, power and self-preservation from black.
The abilities I want to give each character also factor in to their color; for instance, you might think Melisandre would be red (they call her the Red Woman, after all), but she is a sorceress and a prophet and can create shadow assassins, and this will be reflected in her abilities, which are blue and black abilities. So, Melisandre is blue/black.
It wouldn't make as much sense, but I feel like it'd be pretty cool to connect each color to a different God. Red/R'hllor, Blue/Drowned God, White/The Seven, Green/The Old Gods, Black/The Others, Colorless/The Many-Faced God? Like I said it doesn't make as much sense but it's a fun idea.
I will be making the gods (though I haven't yet decided if I want them to be planeswalkers or enchantment creatures, like the gods in Theros), and along the lines of those colors. Depending on the abilities I give them, R'hllor may end up being red/blue and the Drowned God blue/black.