You can change the intonation of a note by changing the tone color. If you make a brighter sound, your pitch will tend to go sharper and a darker tone should help you going lower. This can be very helpful in the low register where the pitch can vary a lot. It is more difficult to do this in the high register but it still makes a difference.
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.