In a story I've recently started writing, one thing that can be done with magic is alter the rate at which someone moves through time. It occurred to me first that the colors they would be seeing would shift because effectively when they are going faster the waves of light are reaching them slower (from their perspective), which would look the same to them as the light having a longer wavelength.
My question is what this would look like from an outside perspective. I'm assuming they are standing still or moving at up to twice normal human speeds (normal human speeds from the accelerated character's perspective), but even so, I'm assuming that the interactions between light and time accelerated matter are different than between light and normal time matter, or at least they act like one of them is doing something differently. I'm tentatively thinking the same sort of hue shift, but in the opposite direction, but I'm not sure if that's actually how that would work.