SlabPappi,
There is no “Contrast” menu in the 1158c units. There is a Backlight menu and a Background menu and you can change the Sonar Color Palette but that is it.

In the 1198 unit in addition to the manus available in the 1158 unit it also has the Contrast menu (in the Si Enhanced menus) but this is only for the Si units. Could this have been what you were thinking of?