Syntax highlighter script

I have been trying to write a simple script in JavaScript to highlight source code in a element such as the code.

Here is the code:

/*
 Syntax highlighter for source code
 Copyright (c) 2007 Samuel Saint-Pettersen
 This script is licensed under the GPL
 http://www.gnu.org/copyleft/gpl.html
*/

function syntaxHighlight()
{      
    var element = "code";    // element for source code
    var attrib = "class";    // attibute for language

    // count all code elements
    var codes = document.getElementsByTagName(element);

    // get contents and class value for each code element
    for(var a = 0; a < codes.length; a++)
    {
        var code = codes[a];
        var contents = code.innerHTML;
        var language = code.className;

        if(language == "boo")
        {
            // define first keywords
            var keyw1 = new Array();
            keyw1[0] = "def";
            keyw1[1] = "print";
            keyw1[2] = "if";

            // colour first keywords
            for(var b = 0; b < keyw1.length; b++)
            {
                var regex = new RegExp(keyw1[i], "ig");
                var matched = contents.match(regex);
                var keyword = matched.toString();
                var repl = keyword.fontcolor("blue");
                codes[i].innerHTML = contents.replace(regex, repl);
            }
        }
    }
}

Problem I have with this code is that after the first keyword is coloured, the loop does not seem to continue. Hmmm... If anyone knows what I'm doing wrong, please leave a comment. Thanks.