Up to this point, Rubens' painting has a limited palette.
I've been excited to move to the red cloak to add a pop of color but the challenge is to nail the red.
Four pools of colors were mixed; darkest with ultramarine blue, semi- dark with Michael Harding Crimson Lake, semi-light/bright also including Crimson Lake, and lightest.
Rubens was a genius in adding a red cloak. Any other color would not have been as effective. I'm sure there are dozens of art experts' articles on the cloak's placement, the significance of the red, and the completion of the circle around Daniel.
As an artist I just know I love the color!