The Fusion/VOIs page in reviewing mode has the layout as illustrated below.
The two tabs Source A and Source B provide the access to the two image components constituting the fusion. So if you would like to adjust the colors, define iso-contours, etc., first select the tab corresponding to the appropriate image, and then use the image controls as usual. The image which is shown as Source A or B can be selected with the upper study switching controls.
The image fusion controls are always available to change among the available fusion methods. To see only one of the images, the fusion balance slider can be moved to the left or the right in the mixing mode. Note: the balance slider can also be moved with SHIFT+drag the left mouse button right/left.
Switching Modes between Reviewing and VOI Definition
For switching to the VOI definition mode (and back from it), select the indicated VOI button. The VOI definition controls appear, and allow the outlining and evaluation of volumes-of-interest.