Warbreaker came from a lot of sourcres. Siri and Vivenna were side characters in a book I never finished. Vasher came from the line that starts the book. No space to post it here, but give it a read. Color magic in came from watching b/w movies. Nightblood came because…well, I just wanted to have a talking sword.
Also, I kid you not, I was talking to my US editor. I’d just finished Elantris and Mistborn, and he said “Your next book needs to have more color in it.”