What distinct quality does the speaker attribute to his beloved's face in this excerpt from William Shakespeare's Sonnet 93?

The distinct quality that the speaker attributes to his beloved's face is that she can conceal her moods completely.

Explanation:

In the excerpt from William Shakespeare's "Sonnet 93" the narrator is mentioning how his beloved's face has the capacity of showing him that she loves him when he knows that she does not longer do so. He is expressing how he is not able to tell exactly what the true mood of his beloved is as she is great at concealing her mood and emotions completely from her facial expressions.