There are large pieces of red flowers on the riverside, and the sun is coming out soon. The morning glow is all over the sky, making the flowers redder and more dazzling than the burning fire. Look at the spring water of that river. It's green as grass and crystal clear as jade.
The sentence "Sunrise makes the river flowers redder than the fire" describes the riverside spring flowers reflected on the first day, which are redder than the flame. It shows the vibrant state of spring, and makes people feel the rich and warm beauty of spring in the south of the Yangtze River. The second sentence says "the riverside is as green as blue". Spring water is rippling and blue waves are thousands of miles away. The poet exaggeratedly described it as greener than blue grass, and this deep blue green is in phase with the fiery red of the river flower reflected in the previous sentence.