Identify the syntax highlighting group used at the cursor
From Vim Tips Wiki
created 2001 · complexity intermediate · author Charles E. Campbell, Jr. · version 6.0
Here's a (what should be a one-line) map to help you tell just what syntax highlighting groups the item under the cursor actually is:
map <F10> :echo "hi<" . synIDattr(synID(line("."),col("."),1),"name") . '> trans<' \ . synIDattr(synID(line("."),col("."),0),"name") . "> lo<" \ . synIDattr(synIDtrans(synID(line("."),col("."),1)),"name") . ">"<CR>
Once known you can override the current highlighting with whatever you want.
If you're debugging a syntax highlighting file (a rare occupation), sometimes you'll wish to know the entire chain of syntax highlighting. For that, see HiLinkTrace.
See also :help synstack()
 See also
Example: Looking at the syntax/vim.vim file's
syn match vimSpecFile "<c\(word\|WORD\)>" nextgroup=...
Put the cursor on the "\(" in the string, press F10:
hi<vimPatSep> trans<vimPatSep> lo<Special>
will show up on the status line. You may envisage the highlighting as a push-down stack of highlighting groups. The "highest" one is the most limited in scope, and is the name of the syntax keyword, match, or region. Generally such a syntax group is linked to a highlighting group. The "lowest" one is the basic highlighting specification, and probably has a broad reach -- in this case, "Special" is a default highlighting group used in 179 syntax highlighting files (vim 6.0) for a variety of purposes.
Syntax groups can be specified as being transparent, so that whatever group they're in is what is used for highlighting. If that's the case, the group mentioned in "trans<>" will be the name of that group, else it is a repeat of the "hi<>" group name.
With the highlighting script (hilinks.vim), you'll get (via \hlt):
vimPatSep -> SpecialChar -> Special
which shows the entire highlighting chain. Thus, a "\(" is identified as being highlighted as a vimPatSep, which is a link to SpecialChar, which itself is a link to Special. Actually a "\(" is a vimPatSepZone region which has vimPatSep as its "matchgroup".