Red, orange, yellow, green, blue, indigo and purple, who is dancing in the sky with color training? What does that mean?

This sentence means: There are red, orange, yellow, green, blue and purple in the sky, and who is dancing in the sky with this rainbow?

In the sentence "Red, orange, yellow, green, blue, indigo and purple", the author borrows the legend about rainbows in folk ci-poetry, and vividly uses the poem "Who dances in the sky with colorful exercises" to describe the gorgeous and blue-sky scenery under the setting sun after rain, which is magnificent and vivid.

This sentence comes from Mao Zedong's Bodhisattva Bodhisattva, which was written by Mao Zedong, a modern politician, thinker and writer, in the summer of 1933. With a cheerful style, it depicts a magnificent scene of colorful cypress land after rain.