Hi Jeff, The capability you need is to make a mask (integer array) that records which region each grid point belongs to. Then you would be able to choose colors for each numbered region. You could define the regions using the "mask" command which can currently only make a new map. This support for masks does not exist yet in Chimera. I intend to add support for masks this year. So the current ways of coloring surfaces are: color zone dialog (color points near markers), surface color dialog (color according to values in a second map, or gradients of a map, or by radius, or height above a plane), or single color. Those methods are for surface/mesh coloring. For solid style volume rendering it is only possible to color according to the grid point values. These coloring methods are limited by the user interface. The underlying rendering code can color a surface or solid in any way you like, though defining other colorings requires writing Python code. Tom