“À night all cats are brown” is a popular expression of the Portuguese language that refers to the idea that all things are alike or the same in the dark.
Interpreting this proverb from a literal and physical point of view, it is understood that in dimly lit environments, things are hardly distinguishable or recognizable by beings humans. This is due to people's inability to see in the dark.
Darkness or low lighting is capable of camouflaging physical aspects that are only visible under certain light conductions. An example is when someone wears an outfit that is faded, and this detail goes unnoticed when in dark places.
According to the scientific explanation, human eyes have cells responsible for color vision, however, in low-light environmental conditions, these cells are less sensitive than those that distinguish intensities from shine.
In other words, the eyes start to capture variations in brightness, making the vision to distinguish shades of black and white. So things appear to be gray or brown in the dark.
However, when this popular saying is metaphorically analyzed, its meaning is related to the idea that in a crowd the particulars are not seen.
Learn about the meaning of others popular expressions.