You might be better set in terms of exploring in a series of questions that could allow you to better understand the topic. The first question I would ask would be for you to examine when you see the color in a prominent setting. What is happening? What is the emotional setting like? What is being revealed? Williams might be using the color as a way for the audience to gauge a better read of the internal thoughts and experiences of the characters. In general, I would think about what the color means and what it might be trying to suggest in the play. Another question that I think you need to ask yourself is to what is the color attached? Clothing, flowers, and other objects can be used to represents a great deal and the use of color might be one of those elements where the connotation is highly important. I think that being able to assess for yourself where the color is used and in what contexts Williams is using the color is going to be important in assessing its overall value and purpose in the play. I think that being able to generate these answers to such questions will help you a great deal in being able to write this essay on your own with your own thoughts on the topic.