Hey Mark, Try adding your measure to color as a discrete measure instead of continuous. We can color on multiple elements as long as they are discrete. Let me know if that works out for you!
I wonder if this is what you are trying to do: https://www.interworks.com/blog/wjones/2013/09/18/create-dual-color-axis-tableau
Each region is a specific color, but within each region there is a continuous scale of color. I believe the dimension region in this example is analogous to the "QEP region" in your data.