To be honest, I would write the story and see what comes naturally to your characters: the colour motif would work if it was aimed at a visual medium, but with prose, there's not always opportunities to describe characters that closely without it coming across as labouring the point. Consciously fixing each character with a colour motif is going to be forced; the best writing comes from unconscious or subconscious choices which dovetail seamlessly with the plot and character development. Even if you outline, it's still a better idea to go with what works for you rather than try to make the decisions deliberately.
Readers will ascribe images in their heads independently of your own. I found this with the Polish names my characters bear as part of the cultural background of my urban fantasy works; however much I give people a pronunciation primer, they're still going to read the names in their head in English pronunciation, so I gave up being concerned about it after listening to my text-to-voice Kindle reading them out. I think you need to be prepared for the colour stuff being much less important than the plotting and characters. The market has turned towards much more naturalistic and gritty ideas; not to say this wouldn't sell if it was really good, but I think you need to take a look at some modern works to get an idea for what people are writing right now and how they go about characterisation.
The characters sound a lot more like archetypes than those you would find in a modern fantasy novel - LOTR was written sixty years ago, and the genre has changed out of all recognition even since epics like The Wheel of Time or Dragonlance - I guess it started changing with A Song of Ice and Fire, but the darker elements have really taken over now and to a reader with a lot to choose from, the old tropey stuff will just come across as old-fashioned. You can keep the ideas, but the stock characters need to be put into a world that feels real, and therefore I think consciously deciding on colour stuff is something that is going to feel un-real.
I mod /r/fantasywriters and it might be worth posting this over there to get some commentary on it.