Below is a photo of a sulfur spinner I took years ago on the Clinch. As you can see from the picture, this is not a typical pale yellow or orange color associated with sulfurs. The reason for this is because there are various species of sulfur present on the Clinch, and depending on what stage of life they are in the colors can range significantly.
I have also posted a link below to an old blog entry I prepared trying to explain sulfurs as they are a primary food source on both the Clinch and South Holston. The Clinch of course being my home river, and South Holston being probably my favorite destination in TN.
I have an entire box dedicated to sulfurs. I have flies in three different body colors in sizes 15, 16, 17, & 18. Also, for each of those body colors I have them in two different colors of CDC wing: gray and tan. I have found in some instances the slightest change in color can make all the difference in the world.