A dark man's a jewel in a fair woman's eye.

The saying depicts a woman who prizes a man described as dark. Calling him a jewel places the emphasis on how precious he seems to her.

The phrase “in a fair woman's eye” makes the judgment personal: his appeal is presented through her regard for him, rather than as a rule about whom anyone ought to find attractive.

If using the proverb to describe attraction, keep the focus on one woman's admiration for one man. Avoid treating “dark” and “fair” as precise descriptions of particular physical traits or as a claim about everyone's preferences.