They're installed in and covered with a material whose texture and color matches the ceiling and walls, behind which they hide.

FORBES: Why do you love it?

It was the first building to use Cor-Ten steel, a material that weathers and changes color over time, and it is his most completely resolved and expertly detailed and executed design.

WSJ: Eero Saarinen, Shaping the Future, at the Museum of the City of New York | By Ada Louise Huxtable