The {syntax-highlighting} tag is for issues with the syntax-highlighting of *TeX or other types of code.
Stack Exchange uses Prettify, a JavaScript library, for syntax highlighting of code blocks across the network.
Improvements to the highlighting for any specific language are most readily obtained by submitting patches to prettify's Google Code project, then (once the patches are accepted) requesting that SE update to a revision of Prettify that includes them.
Improvements to the way Stack Exchange sites integrate prettify may be requested on meta and given the tags feature-request or bug.
For information on available languages and how to use syntax highlighting, see
What is syntax highlighting and how does it work?
