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The setting sun stained the tall rooftops red.
Literal
Evening-sun [topic-は] tall roofs [object-を] red-[adverbially-く] dye-[past-めた].
A painterly descriptive sentence. 夕日 ('setting sun, evening sun') is the sunset-time word, a common poetic motif. 染める ('to dye, stain, color') is metaphorical here — literally 'to dye with color,' applied to light on rooftops. 赤く is the adverbial form of the i-adjective 赤い, modifying 染める — 'to dye [so that they become] red.' Note the [adj-く + verb] pattern: 白く塗る ('paint white'), 長くする ('make long').