If you're looking for a subtle artistic way to control 120V lights, here are some options.
I have to get it out of the way... there is exactly what you are asking for: An electrical switch that is installed in a junction box and beautifully and artistically buried in drywall with no face plate. It's gorgeous, one of a kind, and it's insanely expensive. But if you're building a sort of art gallery in your home, you may be willing to do something like this. Here's a photo of their outlet, because their switch is so subtle it just looks like a circle and gives no sense of scale.
Or, go with a 100% low voltage solution which you can control with switches from automotive or industrial, you can use touch, proximity, whatever you want and you don't need boxes, covers, etc.
.
Some electronic switches have very limited current capacity so you'd have to use a relay as with the next suggestion for 120V lights.
Or, with 120V lights use relays. See this answer to my question about controlling a closet light. You could use the same relay, which would have to be installed in the light's junction box, and a pair of LV wires going to wherever you want the switch. You could use that relay's included magnetic reed switch, hidden in the plaster of your wall, with a clever and pretty magnetic toggle that you design. Or you could replace the reed switch with any kind of switch at all. Doorbells, Automotive, electronic, you could put capacitive switches in the frames of your art, foot plates, you name it.
Or Put motion sensing switches (normal 120V ones in normal boxes) in the ceiling above your art.