What does "selected foreground and background color" do?

[bound-variable]

I changed the --sb and --sf settings, but don't see any changes. I can't discern any semantic difference between the terms "selected" and "highlighted". When I press TAB to move the "highlighted" item over one space to the right, it seems to me I'm "selecting" items to the right. I can press S-TAB to select that item and place it in the filter, but still the --sb and --sf settings don't modify that.