Create a calculated field using the following if statement:
if [Estimated Spend] < [Goal Spend]
Then add the new calcualted field to the color pill and assign "Underspend" to red color and "OK" to another color.
Hope this helps.
This sort of worked (but it applied the color to all of my measured fields, not jsut the 2 i wanted), what do i do to correct?
See if you can add the color for just that particular Mark. Conditional formatting in Tableau is a little tricky with multiple measures. It doesn't work the same way as Excel does.
Here is an link that helps with Conditional Formatting: