[R] How can I draw bars

[Raymond Balise]

I need to make a graphic to show problems on different parts of
chromosomes (think of a graphic showing the number of frayed threads
as colors along different parts of a worn out rope).  I want to draw
bars going from left to right across a page and color different parts
of the bars in different shades.  Each graphic will need to have
several bars of different lenghts corresponding to the different
lenghts of the chromsomes.

Is there a package around that can help me draw custom bars of
different colors?  I am a hardcore SAS guy who is just learning R so I
am mostly clueless.