八識規矩補註 1.12

1.12

此言五識得名淨色者，指勝義而言，體非染法，唯白淨無記性故。五識隨根立名，總具五義，曰依、發、屬、助，如頌言。依者，五義之一也。若作釋者，謂依根之識助根，如根等皆依主釋也，根發之識依士釋也，或云根所發識，又為一例。

Saying here that the five consciousnesses obtain the name of 'subtle form' refers to the ultimate sense: their substance is not a defiled dharma, but of exclusively pure, anivṛtāvyākṛta nature. The five consciousnesses are named according to their bases, possessing five meanings in all: relying, generating, belonging, and assisting, as stated in the verse. 'Relying' is one of the five meanings. If analyzed as a compound: the consciousness that relies on the base, or assists the base, or is like the base, are all tatpuruṣa compounds; the consciousness generated by the base is also a tatpuruṣa compound, or saying 'the consciousness generated by the base' provides yet another example.