Red Green Bible

This puzzle features 19 books with hexadecimal RGB colour codes on the covers. Filling in the colours gives:

Book #8 might be particularly familiar to medical students as the famous Oxford Handbook of Clinical Medicine. In fact, all of these books are Oxford Handbooks, the full list of which can be found at the publisher's website.

The question mark on each book cover correspond to the latest edition of that book (as listed on the publisher's website in 2023). We use this number to index into the subject of its book. If there is no number on the cover, that's because the book in question is in its 1st edition, and we use 1 as the number.

The extracted letters spell COLOUR TEST PLATE NAME, referring to the ISHIHARA plates.