Ordinarily, the world around you is lit by light of many different colors. When this many-colored light bounces off of things, some colors get absorbed, while others get reflected. It’s the light reflecting off objects that give them their apparent color. For example, a sweater looks red because it reflects red light into your eyes.
In this room, there is no red light to bounce off of things and make them look red. There’s no blue light or green light either. With only a single color to absorb or reflect, objects look to be more or less the same color.
The yellowish light in this room is produced by sodium vapor lamps, which are commonly used in streetlights because they’re energy efficient. They also help reduce light pollution problems at astronomical observatories. (Light pollution of a single color is easier to filter out.)
Sodium vapor lamps like the one illuminating this room emit light that is monochromatic, that is, of a single color or wavelength—589 nanometers, to be precise. (click image to enlarge)