Consider that I am creating an interface for a mobile app which shows a list of buttons on the main screen. I can move through the buttons using mobile keypad (feature phones) or screen touch (smart phones). I wonder if I should implement the currently focused button in darker shade as compared to the other buttons? Or a lighter shade would work as well? I mean is there any unwritten UX rule that selected/focused button is always in darker color compared to the other buttons on the same screen?
There is no rule, written or unwritten. All that matters is that: