glBegin ( GL_POINTS ) ;
     for ( i = 0 ; i < num_points ; i++ )
       glColor3f ( red[i], green[i], blue[i] ) ;
       glVertex3f ( x[i], y[i], z[i] ) ;
   glEnd () ;

Where you have the arrays red, green, and blue I believe
those are double's... So I have a few questions about
them. How do you pick the numbers? What's the max and
min? Can you use negatives? Does the max value for red
make the red really dark? Really light? Basically, what
happens to the colors when I pick different values?
Thank you for the help.