On rumination, however, it occurs to me that there are at least three reasons why such a move is unlikely. I've already mentioned one, which is the association of yellow with cowardice. The second reason, as has been pointed out to me elsewhere, is that an animal that curls into a ball or runs away when threatened only worsens the implications. Finally, there's the fact that public admission of the Spanish origin of the city's name is likely to be unpopular given the present political climate in Texas--especially rural Texas--regarding Mexican influence in American culture.
An Amarillo Armadillo
Maybe the folks who live in Amarillo, Texas, aren't really so proud of the fact that their city means "yellow" in Spanish. If I were on the city council, however, I think I'd want to embrace the fact, and move to make Arty here the city mascot.