俱舍論疏 16.9

16.9

The Śāstra says: "This designation 'dark and bright' […] because they mutually contradict"—this explains the name 'mixed'. The phrase "dark and bright" is established with respect to a continuity; it is not that a single karma is both dark and bright, nor that a maturation is both agreeable and disagreeable, because wholesome and unwholesome, agreeable and disagreeable, mutually contradict each other. However, because within a continuity it is mixed with the dark, karma of the desire realm is called dark and bright.