Hi Bill;
I too have seen blond colored rhino horn, and, as you mentioned, it is very similar to wood in its graininess and likewise in its being opaque, with no member of the rhino family having translucent horns.
Another way to tell is to moisten it...if it's rhino horn it will expand, making the hairs individually apparent and giving it a slightly "sticky" feel, as in very fine velcro, one of the prime reasons it was (and still is, thus the poaching problem) prized for hilt material, as opposed to regular horn, which will become slippery.
While the horns of giraffe are less compacted than rhinocerous, they are still used rarely to occasionally, very fortunate for giraffes, while the hoofs of many of the large quadrapeds are very similar to the material found in their horns and could also be easily used for hilting/ scabbard sheating purposes, although they are more commonly used, of course, as "Jello".
Mike