We've seen agaves with that smoky blue coloring but 'Blue Boy' yucca is a rarity. A hybrid with broad, sword-like leaves that are blue- to gray-green at the base, the color morphs to a dusky purple as the foliage begins to arch over. Hardy down to about 10 degrees, this yucca may grow to only two feet tall and wide in the Pacific NW, but over time and given the best conditions, 'Blue Boy' could grow into an upright barrel-like form around five to six feet tall and maybe half as wide. Drought tolerant once established, it can handle all-day or partial sun. Deer and rabbits seem to ignore it, and is relatively pest free.