Color Contrast in Othello

One thing that I started to think about in class on Monday was how Shakespeare uses contrasting colors throughout Othello. The first thing I thought about was the difference in skin color between Othello and Desdemona. Othello is a Moor, making him a darker skin color. Desdemona on the other hand was a Venetian. She is the daughter of a senator, wealthy, and white. Othello is called, "an old black ram" (49) while Desdemona is called, "the fair daughter" (50) by Roderigo. Shakespeare presents the two main characters in different lights. Why does he do this?

The second example I thought of was in Scene V. Desdemona asked Emilia to lay out her wedding sheets on the bed. These sheets I pictured to be white silk; sheets fit for a princess. The handkerchief that was given to Desdemona was also white with strawberries on it. By the end of this scene, Desdemona, Emilia and Othello lie dead on these sheets. The clean, white sheets and handkerchiefs are covered in red blood. 

It seems that Shakespeare uses the color white to represent purity. With Desdemona's white sheets and the handkerchief from Othello, she is surrounded by innocence and purity until she is dead. At that time, the clean sheets are covered in blood. It seems that Shakespeare left us with a vision of blood covered sheets to show a loss of innocence. Was Desdemona's innocence fake the whole time?