Rated 4 out of 5 stars

Review of Xmas 1.0:
Not bad for a work-in-progress. Though the text in the status bar and on inactive tabs needs a better contrasting color.

This review is for a previous version of the add-on (1.0). 

Could it be TMP?

If you are referring to text for unread tabs and you are using TabMixPlus, this is a feature of TMP that you can turn off. I believe, by default, TMP sets the text color of unread tabs to gray, which would of course not contrast with tab backgrounds of Xmas. \r\n\r\nPlease check this setting and send a comment to the support email if this is not the case. All is fine on my end.