Why is my dd tab font color not changing?

DD tabs allow you to change the font color of your menu tabs either in Editor via the popup tool bar OR in the theme code.

If you have changed the font color using the popup tool bar, it will remove any hover color or font color set in the theme code:

Any changes you make to the theme font color will not apply when the font color have been changed using the popup tool. To get the hover effect back, you can delete the exiting content in header text and re-insert it to set it back to default so it will follow the new color change.