It's such a simple cover and not, at the same time. I'm guessing it's all about symbolism.
Butterflies stand for different things depending on the culture. The Ancient Greek word for butterfly means soul or mind. In Japan, they represent a person's soul, but most people see them as a symbol for rebirth or freedom.
Ice symbolizes the barrier between the conscious and unconscious mind. In dreams, it suggests lacking a flow of ideas and thoughts and that you are not seeing any progress in your life. Alternatively, it means you may be feeling emotionally paralysed or rigid and need to let your feelings be known.
And if you wanted to go a step further, you could analyse the shades of blue on the butterfly.