Black Beauty - the first edition
Many thanks to Susanna for sending me this link. It's possibly not a first edition: that was bound in red, blue or green, with the horse's head looking to the right. John Carter (More Binding Variants, Constable, 1938) thinks this is a variant of the first: whether it is or not, it's still a very early edition. A first edition will cost upwards (sometimes very well upwards of £3,000).