What does the first song "Recalling Jiangnan as Green as Blue" mean?

Green as blue: Green is greener than blue grass. For example, the usage is still "Yu", which means more than. Blue and blue grasses, whose leaves can be used to make blue-green dyes.

From Bai Juyi (Tang) "Recalling Jiangnan, Jiangnan is Good", the original text is as follows:

How beautiful the scenery in the south of the Yangtze River is. The picturesque scenery has long been familiar. Spring is coming, and the sun rises from the river, making the flowers on the river brighter than the red ones, and the green river is greener than the blue grass. How can one not miss Jiangnan?

This word describes the spring scenery in Jiangnan, and the first sentence is "Jiangnan is good". The word "good" includes all the good points of spring scenery in the south of the Yangtze River, and the author's praise and yearning are also among them. In Bai Juyi's works, the spring scenery in the south of the Yangtze River has been colored since the first day, and the flowers and rivers in the river have formed people's imaginary pictures because of the way of dry dyeing. Colorful and rich, almost no need for more associations. Spring scenery in the south of the Yangtze River has come to my face.