Danielle, you need to post a packaged workbook, "save as", tbwx.
As far as I've been able to determine, Tableau colors marks, not headers. The general reasoning seems to be that coloring headers can make visualizations more difficult to interpret when every row could have a different color.
However, one way around this is to create a dummy measure, then use the measure label as a dummy header row. Here's how to do this:
Create a calculated field with a value of 1 and put that on your Columns shelf to the left of the measure. Set the label of the field to the desired text, and set the color of the field appropriately. The "measure" now has the text of the field. You then need to do some work with the field formatting to remove the 0 axis, tick marks, and white out the 0 label.
I did this for the High Grade field in the Special Education: Percent Classified worksheet in the attached workbook (Tableau 7.0 format) and I imagine that if all the headers were colored this way that the graph would be harder to read.
An alternative would be to do something that is more of a highlight for some values, in other words just color the Charter or District, and leave the other black. You can see this in the Special Education: Highlight worksheet.
A third alternative would be be to create a label to highlight either Charter or District (or both), that would show up regardless of the particular Percent value. You can see this in the Special Education: C/D worksheet.
Finally, you could get a tiny bar by changing the Axis of the Percent measure to be fixed with a minimum value of -0.5 or so. You'd then have a very small indicator of Charter or District for zero values. You can see this in the Special Education: Axis worksheet. My opinion is that this is probably the easiest to understand option, other than adding a Row header for Charter/District.
Here are a couple of other posts on different formatting options that I've used:
chartersegregation2.twbx 318.5 KB
Thank you for all the help. I think I might go with a combination - change the axis to -5, but also add the charter/district label to highlight the charters using a "*" instead of the "C". Seems a little less intrusive. Thanks again.