DOCBOOK-APPS: Changing the color

I'm using the docbook slides DTD.  The 
material is for a computer programming class and I have lots of code snippets 
that I render with <screen/> tags.  What I'd like to do is be able to 
highlight a line of code within a <screen><screen/> set of 
tags.  I have tried <emphasis> and it works but the italics don't 
stand out very well.  Is there a way I can change the color o the font 
using <emphasis> or the like?

 

Cheers

Eric