This is the 3304th most frequent Portuguese word.
escuro
Dark.
Here, 'escuro' is used as an adjective describing the sky, indicating its lack of light due to the approaching storm.
O céu ficou escuro antes da tempestade.
The sky became dark before the storm.
In this instance, 'escuro' is again an adjective, applied to the room to emphasize its insufficient lighting, suggesting a solution.
Este quarto é muito escuro, precisamos acender uma lâmpada.
This room is very dark; we need to turn on a lamp.
Here, 'escuros' is used as an adjective describing 'tons' (shades), reflecting a preference for colors with lesser brightness or light.