The sunset clouds are like ribbons of silk — truly 'who holds the colored silks dancing in the sky?'
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From 毛泽东《菩萨蛮·大柏地》(Mao Zedong, 1933), written returning to a former battlefield: 赤橙黄绿青蓝紫，谁持彩练当空舞？雨后复斜阳，关山阵阵苍 (Red orange yellow green cyan blue violet — who holds the colored silks dancing in the sky? Rain gone, the slanting sun returns; pass after pass in gray procession). The first line lists the seven colors of the rainbow; the second is the question it suggests.
usage
谁 is read shéi in poetry (also written shuí). 彩练 literally = 'colored silk ribbons,' here standing for the rainbow. The line is a stock quotation for describing any long, brilliant, sky-spanning sight.
