First off, let me comment on the beauty of the LOTRO mounts: their authentic appearance, and the great variety of colors and breeds available.
As lower-level players, we could "look" at the mounts before we made our purchase. Remember the first time you ran up to Hengstacer Farm to inspect the choices; they were all standing in stalls near the vendor and you could pick out the color that you liked best. This has also been the case recently for festival mounts. In addition, there are some zones, such as Evendim, where you can "preview" your purchase (i.e., the Dark Chestnut reputation mount stands next to the vendor).
Unfortunately, this is not always the case when you get further into the game. Sometimes the reputation mount is in the vicinity (but sometimes it is not), and where there is more than one choice (such as in Mirkwood or Angmar) it is never clear which is which. Personally, I always double-check online resources before I make my purchase.
However, there are games out there that allow players to "preview" mounts in an inspection window just like cosmetic clothing. Although this would be a welcome addition, I understand that it may be difficult to achieve. This being so, why not position an example of the reputation mount in close proximity to the vendor in all cases? To add to realism, the horse could be grazing or feeding in a stall, or there could be an NPC grooming it as we see in Galtrev.
Running LOTRO on a Mac Pro 2x2.66 GHz Dual-Core using Bootcamp