Form the middle four columns by (mostly) symmetry first. In columns 7 and 14, the 3/4/3's are in the middle and adjacent to one another. (C7, R5 - R7, R9 - R12, R14 - R16)
Complete guessing. Not TOO difficult if you work from the center out and just... draw based on the title, but... not very well designed. Especially since inverting it WOULD be solvable with logic, and would fit the motif nicely considering Snow is White...