The rhyme is yŏ/chŏ; tones match. There is a problem in the exegesis of the first line. “The Diamond Mountains gladly shed their beauty” seems a viable alternative.
Bones is a reference to skeleton, which is the winter name of the Diamond Mountains. Joy translates the thrill of hŭng, which is the buzz of excitement that accompanies the apprehension of beauty.
Gladly I leave the Diamond Mountains;
green mountains are reduced to bones.
A rider on a jet black horse
hesitates in the absence of joy.
There are other texts that substitute donkey for horse and characterize the animal as lame. One text substitutes manyak (if) yak for (joy) rak, creating an alternative version:
If the Diamond Mountains lose their beauty,
green mountains will be but bones.
The rider on his black horse
will hesitate in the absence of joy.