First of, welcome to the forums!
I hope you find the information here very useful.
In general, this type of formatting was fairly difficult to achieve in Tableau 7 and previous versions. This, however, is easy in 8. In fact, an algorithm has been added to Tableau 8 that determines automatically whether a label should be white or back based on the color of the region in which it lies. See the attached screenshot.
Hope this helps,
8 Formatting.png 107.2 KB
Hello - I came across this post in searching for an answer to the same question. I'm working in Tableau 8 however it seems the labels often do not display as white when they should. Is this a known issue? Or is there a setting I need to activate to trigger the color assignment? (See attached) Thanks!