I listened to a lot of different kinds of music when I was writing GILT, most of it modern. I usually get inspiration in the car or while out for a long walk (or run), and I usually listen to music while I do those things, so often music from the radio will get churned up in my mind with plotlines and character flaws and even full scenes. But during the year it took me to write and revise GILT, through the several incarnations of the character (who was originally called Thomas), this song was always William's.
It's hard to explain why. Some of it could be that Chris Martin reminds me of William (crossed with James McAvoy). But I think more of it has to do with intention. The idea that love is a bright, shiny yellow. The idea that the expression of love can be something as simple as pointing out the color of the stars. The idea that no matter what, William thought Kitty was beautiful. We can all hope for that kind of love, can't we?