I just wanted to add that if you set the Delphi calculation parameters to also create a Grasp surface, and then use the Grasp surface for display in DelphiViewer, the neutral parts are opaque white. This is true at least in version 1602 and a few preceding versions. In the next release, you can control the color and opacity levels for positive, neutral, and negative potentials explicitly. Elaine =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Elaine C. Meng, Ph.D. Babbitt Lab and Computer Graphics Lab meng@cgl.ucsf.edu http://www.cgl.ucsf.edu/home/meng/index.html =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=