Directly related: Angry Atoms.

At what point in the piling up of colorless particles and forces does an actual shade of blue magically spring into existence?

I have no idea. I don't pretend to deserve a Nobel prize. But I am reasonably sure that the colorless particles and forces we need to look at to figure that out reside in the brain, not in EM radiation of a specific wavelength.

I'm also pretty sure that however the experience of seeing blue springs into existence, no magic is involved.

That's it? That's all it took to make you start hiding behind the Sorites paradox? That was easy.