I actually have to give it to Boaz because, while Dany calls her horse her silver, and drogo's horse was referred to as his red stallion, the Dothraki do not name their horses. the clinching point is that, in the books, when danny calls her horse her silver, the word silver is not capitalized, which would indicate it as a descriptor rather than a name.
Boaz has it with Honor, Glory, Dancer, Stranger and Dunk's horses, though I can neither confirm or deny that those are correct, being as that I don't know the Dunk and Eg stories well enough.
the 5th horse I was thinking of is Smiler, Theon's horse.
So, to Boaz with a technicality.