Richard buys Rose a palomino horse and they call it Heart of Gold, so the song title for this scene had to be Heart of Gold by Neil Young.
If you want to read more about ‘Heart of Gold’ and what happens when Rose rides out with Richard you can download the book here: Richard Liveth Yet.
Image of Neil Young: By photographer Mark Estabrook from Sedona, AZ, United States AKA Markestabrook at en.wikipedia. [Copyrighted free use], from Wikimedia Commons
Image of palomino horse: By KissGirl (Own work) [Public domain], via Wikimedia Commons