Chimera Commands Index -- not implemented in Chimera --
(however, yon intensity can be changed in the Effects section of the Viewing Tool)

Usage:
intensity hither_value [yon_value]

Intensity changes the value of the intensity at the hither and yon clipping planes. The values range from 0 to 1. Default values are 1 for hither (maximum intensity) and 0.2 for yon (minimum intensity). Note that the location of the hither and yon clipping planes may be changed with the clip command or by manipulating the Side View.

See also: clip