Hi Huy, Currently a surface can be colored with the color zone dialog with only one radius. If you want to use multiple radii you can change a couple lines of the Color Zone Python code as follows. Edit the file chimera/share/ColorZone/__init__.py using any text editor. (On the Mac this is Chimera.app/Contents/Resources/share/ColorZone/__init__.py). In the color_piece() routine around line 66 you'll see the line rgba[:,:] = p.color Add two more lines after that so you have rgba[:,:] = p.color if not p.vertexColors is None: rgba[:,:] = p.vertexColors Make sure the indentation is as shown since indentation level is important in Python. Next in the color_zone() routine near the top of the file (line 13) find the lines if auto_update: zone_updater.auto_zone(model, points, point_colors, distance) and put a # character in front of these two lines. # if auto_update: # zone_updater.auto_zone(model, points, point_colors, distance) Then restart Chimera and you can use color zone repeatedly on the same surface with different radii and different markers selected. I tested it with Chimera 1.2539 (daily build) but it should work with the 1.2470 production release. The first code change you made preserves the current coloring of the surface when a new color zone is added. The second change you made eliminates automatic coloring updates when the surface shape or coloring radius changes. Without the second change if you move the color zone dialog slider to color using a new radius it will update the radius of your previous color zone coloring which you do not want. With these changes Chimera sessions will not save the color zone coloring in session files. More significant changes would be needed to allow saving the coloring in sessions with multiple coloring radii. It is our intent to improve the Color Zone code to make multiple radii work. It is on our Chimera plans web page item 37. http://www.cgl.ucsf.edu/chimera/plans.html Tom