Interesting. I couldn't understand why the HSV formula would not result in an unwanted change in colour. But I don't really understand why it would, either!

What focal length lens did you use for this render? I only ask because the views of the spheres are at quite different angles, made clear by the difference in shadow size and the position of the right-hand specular highlight. For a better side-by-side comparison of shading I would be inclined to use a much longer focal length.

Obviously, this makes no difference to us seeing the colour shift on the HSV corrected sphere.

:O)

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)