The X11 graphics did not display colors correctly when CHARMM was compiled for a 64-bit OS, such as Linux x86_64 machines. A simple fix has been found for this, which can be easily applied to most CHARMM versions. In the common block file fcm/graph.fcm change (ca. line 97):

      INTEGER NGRSEL,IGRZLEV,COLOR_MAP,MAXPVO,NPVOBJ,KPVOBJ

to:

      INTEGER NGRSEL,IGRZLEV,MAXPVO,NPVOBJ,KPVOBJ
      INTEGER*4 COLOR_MAP

The automatic promotion to INTEGER*8 was causing type mismatch problems when the COLOR_MAP array was passed to a C routine. This fix can be applied to c33b2 and earlier CHARMM distributions.

Rick Venable
computational chemist