If you are referring to the source rather than the output you could use a good find and replace tool to do this. However the text string you'd have to use to find the red text could be tricky. The problem is that if you have red text some of which is bolded and some of which is bolded and italicised you'd have two different text strings to find. There would be an element of analysis to be performed of your HTML to enable you to establish which search strings to find.
This blog post has details of two of the most pouplar find and replace tools on the matket.
Read the RoboColum(n) for mutterings on RoboHelp, Technical Communication Suite and technical communication.
Thanks Colum, most helpful
RH's own Multi-File Find and Replace may work for you. Personally, I prefer using either FAR HTML or the latest NotePad++ to search for source code across multiple files.