The selected cell is sort of a bluish-gray. If you change the selected cell's color, it's still bluish-gray.
TListView and other controls have a property "Hide Selection" where the selected item loses selection colors when the control loses focus.
What would be better is to have an alternate form of "selection" where you can switch between the current way, and also select some kind of frame instead so the BG color isn't hidden by the selection color. Maybe have a "Selection Frame Margin" property that defaults to, eg., 3 pixels, as well as a "Selection Frame Color" that's used unless the BG color is close to it, then it changes to something with greater contrast, or a hash pattern.