Read the Brut article by Chris Colby in the Jan/Feb 2019 Zymurgy magazine. In the article he recommends 0.13 oz of finely crushed black malt in a 5 gallon batch to clarify. On page 83 he writes "... in my experience it clarifies light-colored beers noticeably."
Page 63 "An old homebrewer's trick may also come in handy. If you crush roughly 0.25 oz (7.1g) of black malt per 5 gallons (19L) batch and stir it in the mash, your light-colored beers will turn out clearer. The small amount of black malt does not add as much color as you might think (or as your recipe formulation software calculates), but in my experience it clarifies light-colored beers noticeably."
The 0.13 oz black malt is noted in the "I Am Broot (All Grain)" recipe on page 61.
New one on me. First time I'm hearing/reading such a claim. Other's thoughts on this matter?