Generally speaking when you want your user to have any input or decision a parameter is most likely where you want to try. Create a parameter with two values (I.e. Name - Break out by ethnicity; Values - Yes, No). Then you can create a calculated field like "If [Break out by ethnicity] = 'Yes' then [Eth] else 'All' end" Now take the new calculated field and put it in the color field like you have the Eth. Make sure you Show Parameter Control so the user can select which they want to see.
Thank you for the reply! This gets me exactly what i need!
That's great Andrew! If you could mark the answer as correct it would be greatly appreciated!