If data-highlight is used alone without data-highlight-color, data-highlight-color is set to blue.
If data-highlight-color is used alone without data-highlight, data-highlight is set to an empty string ( "" ) so the current domajax element will be highlighted.
When you are using data-highlight alone, it is an alias for data-highlight-success. But, if you are using data-highlight and some data-highlight-color-(event) options, then data-highlight will apply for the (event)s specified, and no more for success event if data-highlight-color-success is not defined.
If data-highlight-color-complete and data-highlight-color-success (or failure) are defined, if the ajax call succeed, the data-highlight-color-complete color will be used. In fact, both highlights will be made but as jQuery executes complete callback just after success, there will be no time to see the success color.