Underneath the color mapping buttons is a `gating region' that can be changed by clicking on the color strip. The active region (selected colors) is indicated by a narrow black bar to the left of the color template. The `up-' and `down-' pointing arrows determines whether the upper or lower portion of the gate is to be changed. The `R' button further down resets the window to its full range. One can switch off late or early tubes interactively with this tool.