suggestion

Below really is not a good translation. But I tried to emphasize the 动感。 '浮雲歸晚翠' really brings in a motion picture. Also I tried to emphasize the contrast.

"Once seeing off the color clouds drifting into the lavish greens in the evening
Now only sadly watching the sun sinking amid autumn sounding"

I also noticed that using 'once' and 'now' really does not bring the time separation. The scenes painted in first and second line are hundreds of years apart. But I have no good way to translate.

I admire your courage to work on the ancient Chinese literature translation. It is really a hard task. It is beyond me. But I like to discuss with you and I will learn from the discussion myself.