This is the 1199th most frequent Polish word.
biało
"Biało" means "white" (adverb) in English.
The word 'biało' here is used as an adverb to describe the state of being covered in white, specifically snow.
Za oknem zrobiło się biało od śniegu.
Outside the window, it has turned white from snow.
In this sentence, 'biało' serves as an adverb to describe the general appearance or condition of the kitchen being white.
W kuchni było biało, ponieważ wszyscy piekli pierniczki.
In the kitchen, it was white because everyone was baking gingerbread cookies.
Here, 'biało' is an adverb describing the way everything appeared, emphasizing the effect of the fog.