The tale uses opposing imagery-the natural, warm beauty of the rose verses the stark symmetry of mirrors and ice/snowflakes. The mirror in this tale is unusual in that, while mirrors usually tell the truth (such as the mirror in "Snow White" that is bold enough to bluntly tell the Queen when there is someone more beautiful than she), this mirror is deceptive-it distorts reality, causing beautiful things to seem ugly. (In fact, I sometimes thought of this mirror when I was in my first trimester-when foods I usually loved became disgusting to me and activities I enjoyed lost interest for me because of the constant nausea-I felt like I could relate to Kay).
Mirrors usually represent vanity in stories. The theme of vanity is also developed in "Snow Queen" by the reference to Gerda's red shoes. When she goes to search for Kay, she intentionally puts on her new red shoes that Kay has never seen before, but when she goes to the river she is willing to sacrifice her prized possessions to gain information about his whereabouts (but the shoes are returned to her because the river does not know where he is). Interestingly, this tale was written just four months before Anderson wrote the infamous tale "Red Shoes" in which the desire for the colored footwear is completely and repeatedly seen as selfish.
From the "Snow Queen" section of the Fairy Tale Fashion exhibit at the Fashion Institute of Technology. Far left; white fur cape by J. Mendel, second to the left; not in the book, second to the right; Alexander McQueen Fall 2008 dress inspired by snowflakes, far right; Tom Ford Spring 2014 dress that imitates shards of a broken mirror
Red Morocco leather shoes, from 1800-1810
Although, it was more of a natural assumption at the time to associate red shoes with luxury, since red dye was more difficult to produce, and therefore more expensive, so red was a color only the wealthier could afford. But it seems that illustrators to tend to intentionally bring out the contrast in warm colors associated with Gerda, her friendship with Kay, and her journey to find him, as opposed to the cold realm of the Snow Queen. See Arthur Rackham's illustration of Kay and Gerda in their garden, and Edmund Dulac's image of Gerda at the old woman's house: