You need to differentiate between two aspects: highlighting of text
within a org buffer and what happens to text when exported. In the new
exporter, I don't think you can implement anything that covers both use
cases.
I am not entirely sure what it is you want. If you want just one of
these, for the former, font-lock-add-keywords is probably what you want
to pursue. For the latter, you probably want to use a macro with
@@latex:...@@ and/or @@html:...@@ code embedded in the macro to export
the text the way you want it, as in
#+macro: coloured @@latex:{\color{red} $1}@@
This is some {{{coloured(text)}}} when exported.
HTH,
eric
--
: Eric S Fraga (0xFFFCF67D), Emacs 25.0.50.1, Org release_8.3beta-1293-g985420
