法華義疏 6.39

6.39

丹是赤色中之盛，由深定故多所發生，其功顯灼如丹色也。又釋古人合神丹為枕，令得長靈之壽，譬入涅槃則常樂我淨也。

Cinnabar red is the most vivid among reds. Because of deep concentration, much is brought forth; its efficacy is bright and blazing, like the color of cinnabar. Another explanation: ancient people compounded divine cinnabar into pillows to obtain longevity and immortality, symbolizing that entering nirvāṇa brings permanence, bliss, self, and purity.