In Act 2 Scene 1 of William Shakespeare’s The Merchant of Venice, the Prince of Morocco tries to impress Portia in order to marry her. He tells her that she should not dislike him because of his dark complexion or skin. He says that he has a dark complexion because he was raised in a place, which is close to the sun. (As we know, sunrays or UV have a skin-darkening or tanning effect).

The shadow'd livery of the burnish'd sun,
To whom I am a neighbour and near bred

Because of the cold weather in the North, most people born there supposedly have a fair complexion (and the Moroccan Prince wants to compete with the fairest man of the north). 

Bring me the fairest creature northward born

He claims that even the courageous and fearless men get terrorised seeing his dark, rough look and the prettiest ladies of his country love his skin colour (and, yet, he would not mind changing it to get Portia’s love).

I tell thee, lady, this aspect of mine
Hath fear'd the valiant: by my love I swear
The best-regarded virgins of our clime
Have loved it too:

Phoebus describes the Sun God or Apollo. Phoebus’ fire is, then, sun’s fire or heat.

To prove that his blood is the reddest (redder than the fairest man of the North), the Prince says that he would make an incision or cut on his body.

And let us make incision for your love,
To prove whose blood is reddest, his or mine