Sourdough getting too brown
Some people find very brown crusts on sourdough desirable. Judging from the first picture at your link, the author of your recipe may be one. If you don't, one thing to try is to remove the loaf from the cocette something like 10-15 minutes before the end of baking time. This way the crust isn't directly exposed to the heat of the cocotte itself and will brown less. (We started doing this when the bottom crust was getting too dark by the time the top crust, after removing the lid, was browned to our liking.)