I would guess by reflecting light off something silvery, eg, a wall painted in metallic silver paint.

That's not how colored light actually works. (That's the joke!)

There isn't a silver "color" of light, it's a visual phenomenon that warps and reflects the color of the environment around it.

So unfortunately there are no silver colored light bulbs (except for using a silver coating to block or reflect the light).

Maybe it's that shiny reflective things like disco balls are therapeutic, imparting modernity, sophistication, intuition, reflection, coldness, or disco fever.

Although they are both forms of environmental modification, light therapy is different than color therapy. Light therapy uses e.g. daylight to boost affect. Color therapy uses e.g. silver paint to prime cognition.