p-amino phenol hydrochloride, which is the main developing agent in rodinal, tends to have this brown color in the final image. There are several important factors when it comes to final image color. Even a new agent from another factory can cause color-tone shift. Other things as simple as the water you use +++, etc.. The best neutral result "with the developers used": I would stick to a developer [1st & 2nd] with a high concentrate of HQ and sulfite. Most films will have a good 'neutral' with such a developer.