To insert code samples into your articles in joomla, you use the pre tag like this:

<pre xml:lang="xxx"> your code goes here </pre>

You can use any of the following languages for colorizing your code in articles. 
 

recital, abap, dos, lotusscript, rails, actionscript3, dot, lscript, reg, actionscript, d, lua, robots, ada, eiffel, m68k, ruby, apache, email, make, sas, applescript, fortran, matlab, scala, apt_sources, freebasic, mirc, scheme, asm, genero, mpasm, scilab, asp, gettext, mxml, sdlbasic, autoit, glsl, mysql, smalltalk, avisynth, gml, nsis, smarty, bash, gnuplot, objc, sql, basic4gl, groovy,

ocaml-brieftcl, bf, haskell, ocaml, teraterm, blitzbasic, hq9plus, oobas, text, bnf, html4strict, oracle11, thinbasic, boo, idl, oracle8, tsql, caddcl, index.html, pascal, typoscript, cadlisp, ini, perl, vbnet, cfdg, inno, per, vb, cfm, intercal, php-brief, verilog, cil, io, php, vhdl, c_mac, java5, pic16, vim, cobol, java, pixelbender, visualfoxpro, c, javascript, plsql, visualprolog, cpp, kixtart, povray, whitespace, cpp-qt, klonec, powershell, winbatch, csharp, klonecpp, progress, xml, css, latex, prolog, xorg_conf, delphi, lisp, providex, xpp, diff, lolcode, python, z80, div, lotusformulas, qbasic