What a colophon is for
The note at the back of the book that tells you how it was made — and why that is generous.
The colophon is the note at the back of the book that tells you how it was made — the type, the paper, the press, sometimes the name of the person who set it. It is the least commercial page in publishing and it is the one designers turn to first.
It is generous. It hands the method to the next person instead of hoarding it, on the assumption that the method is not the valuable part. Anyone can know that a book is set in Doves Type on 120gsm mould-made; almost nobody can do it well. The secret was never the ingredient list.
If a colour ever fails contrast, the page will show the failure rather than the intention.
It is also an accountability device. Writing down the stock means someone can hold you to the stock. Writing down the contrast ratios means the ratios have to be true. A practice that publishes its own materials has fewer places to hide, and that is a good pressure to be under.
This site has one, at /colophon, and it is not decorative. The ink library on it is measured at runtime. If a colour ever fails contrast, the page will show the failure rather than the intention.