I〔一つの色〕one color,《英》 one colour;〔他の色と混じらない〕a solid color
赤一色のじゅうたん
a solid-red carpet
壁は白一色に塗られていた
The wall was painted all in white.
II〔一つの傾向〕
町はどこへ行っても選挙一色だった
It was impossible to forget about the election no matter where you went in the town./The whole town was completely caught up in the excitement of the election.