The first line is a classical comparison, the eyes being the window to the soul and when he says that her eyes are nothing like the sun it could imply that her soul is dark. Red is the symbol of passion and vitality, something that he could be claiming this woman's lack with that statement. In Shakespeare's time the skin should be white as snow and breasts are a symbol of femininity, by saying her breasts are dun, which is a shade of brown, he deprives her of what was the idea of feminine beauty in his time. Wires in this context should not be confused by the idea of industrial wires we have today, hair was often compared with golden wires, but the mistress has not golden wires but black ones growing on her head. These four lines describe her physical appearance as the author sees it, giving the impression of a vile and cruel creature, not deserved of love. It also gives her a very human nature, poems of love speaks of their subject as something divine, without flaws and perfect in every sense.