‘Frosty’ Canadian hemlock is not named in honour of the snowman, but rather for the white colour of the new needles on the tips of the branches. As you can tell, this phenomenon is not well-displayed by this photograph. Instead, the focus is on the cones and the shadows from winter’s low sunlight.
I have the impression that the majority of conifer cultivars originate as a selection of a physical variant that is somehow different from a typical plant in the species, but if someone with more knowledge wants to qualify or dispute that assertion, please add a comment. As a comparison, though, you might recall from the entry on Gladiolus flanaganii that the thirty thousand cultivars of Gladiolus are virtually all due to hybridization and breeding.
Since I suspect that conifers might be on your mind this month, you might like to spend a little bit of time browsing around the site of the American Conifer Society or browse through the garden’s conifer discussion forums.
Botany resource link: “hamadryad”, a member of the garden’s discussion forums, submitted this article about a study from the University of Washington–“Wildflower seed mixes include some wicked bloomers“. From the article: “When growing 19 such packets of wildflower mixes, however, University of Washington researchers found that each contained from three to 13 invasive species and eight had seeds for plants considered noxious weeds in at least one U.S. state or Canadian province.”