Hello,
You need to add text WordFragments as cell values, that allow to use these options to set colors: color and highlightColor.
We recommend you to read the available tutorial about WordFragments on:
http://www.phpdocx.com/documentation/practical/wordfragments-and-wordml
And the API doc and the available examples in the package of these methods:
http://www.phpdocx.com/api-documentation/word-content/add-paragraph-text-Word-document-with-PHP
http://www.phpdocx.com/api-documentation/word-content/add-table-Word-document-with-PHP
Although working with WordFragments is very easy, after you have puchased a license, the dev team can send you a simple sample to illustrate how to do it.
Regards.