Thou blind fool, Love, what dost thou to mine eyes,
That they behold, and see not what they see?
They know what beauty is, see where it lies,
Yet what the best is take the worst to be.
If eyes, corrupt by over-partial looks,
Be anchored in the bay where all men ride,
The speaker is well aware of the conventional ideals of beauty—not only of red lips, blonde hair, fair skin, but also of chastity and virtue. But mischievous Cupid ensures that his perceptions are distorted, so he desires this undeserving woman who lacks inner beauty. 
 This links with the comment “In the old age black was not counted fair” in  Sonnet 127 .
Sonnet 137