俱舍論記 28.39

28.39

「由彼色微至亦名無黃」者，大眾部等答。由彼色微故名無色，引喻可知。

As for "Because that form is subtle... it is also called 'non-yellow'": the Mahāsāṃghikas and others reply. It is called 'formless' because that form is subtle; the adduced analogy is clear.