https://phys.org/news/2019-01-bright-laser.html

In order to produce different colors, the laser power is adjusted from 1 to 10 mW. The laser power corresponds to different amounts of heating, which reshapes the gold nanoislands in such a way that they reflect light of different colors. Yellow is produced at low powers, green at intermediate powers, and red at high powers.

The method also produces different results depending on the laser's polarization (light waves are polarized when they are restricted to vibrating only in certain directions). When the laser light is linearly polarized, the colors are clearly seen only when illuminated by light of the same polarization. Circularly polarized laser light, on the other hand, produces polarization-independent colors that are visible using light of any kind of polarization as well as unpolarized light.