Protein Explorer can create a solvent-accessible surface and color it by molecular electrostatic potential (MEP). However, as the comparison below demonstrates, a much better rendering is available in the free WebLab Viewer Lite. Therefore if you plan to do much work with MEP we recommend using WebLab Viewer. The results shown below from GRASP confirm that MEP coloring is generally correct in Chime (Protein Explorer) and WebLab Viewer.
To generate a MEP-colored surface in Protein Explorer, go to Advanced Explorer and click on Surfaces.