Is it possible to build a syntax color enhancer plugin?

I want to syntax color some special text fragments in HTML, namely those used by StringTemplate. Is it possible to add some extra syntax checking using a plugin? The builtin syntax colorizers for HTML, JSP etc can't be modified although that would be the easiest since I still want the normal colorization as well.

StringTemplate's information could be identified using some regular expressions, though I have no idea how a plugin for editor syntax colorizing works, so it might be too slow. Example are

$something$
$something:template(arg=x)$
$something:template:template2$
etc

StringTemplate.org