This is the 6395th most frequent Spanish word.
blancas
"Blancas" means "white" (feminine plural).
Here, 'blancas' is an adjective agreeing in gender and number with the noun 'casas' (houses), describing them as white.
Las casas blancas se ven hermosas bajo el sol.
The white houses look beautiful under the sun.
In this sentence, 'blancas' is used metaphorically as an adjective, describing the words as pure or innocent.
Sus palabras blancas mostraban su inocencia.
Their white words showed their innocence.
'Blancas' again is functioning as an adjective, emphasizing the high degree of whiteness of the shirts, with 'muy' intensifying the descriptor.