I love visuals so I would ask what the visual differences of each realm are?
All right! So, the physical realm looks very similar to the world we Earthlings see around us (though of course with my invented fauna and flora and the local architecture, etc.) I imagine the colours as very vibrant and varied, especially in wealthy locales, since the use of weather magic means droughts and destructive flooding or storms are less frequent, and the use of plant magic means not all flora is native to the area or climate.
I'll describe the soul realm from the perspective of a trained user of Light magic, because they're the only ones who can actually see it. It's a bit like a veil or an overlay over the physical realm, in that you can still see the plants, architecture, people, animals, etc. that you see in the physical realm, but their edges are a little hazy and their colours are a little dimmed. Everything is softer and feels slower, even though it isn't actually moving slower, and shimmers with a constant ambient glow that's sort of twilight-strength, no matter what time of day it is. Brighter streaks of colour show up where magic is being done or has recently been used. For example, the hands of the lady who just used fire magic to light the fire would be glowing scarlet, and golden pawprints across the grass might show where a user of animal magic shifted into a cat and leapt off into the forest.
Users of light magic don't see the soul realm all the time, only in flickers here and there or when they choose to. It's a bit like unfocusing your eyes, and then you see this other layer.
As for the spirit realm, no human can see it, but if they could they would see the true forms of people (uninjured, un-shifted) wrapped in a world of swirling mist like a moving sunset. They might also see spirit creatures, but I haven't decided what these look like yet.
