WordPress nav menu

site: https:// nashvilleryanwhiteparta.com

I am running the Thesis theme and using the WordPress nav menu.
I would like to change the color of one tab on the menu so that it is always red.
I have tried multiple resources via Google and the WordPress forum and am unable to make the change.

I have tried targeting the menu tab #, assigning a unique css to the specific menu tab all to no avail.

I have limited coding knowledge and need help. Any assistance in how I make this work is greatly appreciated.