Changing Menu Selected Color

To change the color of the selection indicator on the bottom bar of the app menus, in App Designer, navigate to the Menu Bar menu of the Style menu, and change the color in the Bar Color - Selected selector. You can select one of the palette colors, or specify a custom color.

Changing the color of the selected menu indicator

For example, notice the effect of changing the default selection color (light grey) to red:

Changing the selected color of the menu from light grey to red