[texhax] beamer error: undefined color

[Fehd, Ronald J. (CDC/CCHIS/NCHM)]

I have used beamer in the past
and upon the urging of PracTeX presenters in 2005 and 2006
have downloaded the updated packages:
* beamer 3.06
* pgf 1.01
* xcolor 2.09

per beamer instructions in beameruserguide.pdf of 10/23/2005
I tried to pdfLaTeX examples\beamerexample1.tex

I am quite frustrated at the following hax
to fix an undefined \XC at mcolor
\makeatletter
\def\XC at bcolor{blue}
\def\XC at mcolor{blue}
\def\XC at ecolor{blue}
\makeatother

and this error
%! LaTeX Error: Undefined color 'green!50!black'

Q: how do I trace the variable whose undefined value is
'green!50!black'?

Ron Fehd  the macro maven  CDC Atlanta GA USA RJF2 at cdc dot gov