Si is a contamination of the pure visual experience of the environment. Normally I don't separate these things, but by forcing myself to see the environment purely visually (things, colors, stuff), i realize that there is a contamination. Si itself is not visual, but it comes together with the visual experience. It gives a certain character to the things we see that is hard to describe.
This is only about the visual experience, but it works the same way with comfort etc.