Mu Ye is a representative poet of obscure poems, so his poems are obscure, implicit and full of implications.
Not everything in the sun is sunny /
Not everything in the dark is dark /
The general idea is:
Not everything in the sun is decent, progressive and energetic.
not everything in the dark is corrupt, backward and insidious.
The following "sunshine" and "darkness" are both puns, which contain intention and innuendo.