Sorry I can not give more details, but all I remember is a brown horse (or black) that he grew wings. I remember specifically how the wings came out of the body, so it still had feathers.
I think the horse (or pony) was next to a farm that had a white picket fence.

The film is in color and before 1990. Obviously not Clash of the Titans.

I do not speak English, so I apologize for any errors. Thank you!