This gets me every single time. I also have seen plenty of screens where buttons are given a "selected" state (e.g. a dark blue background), but it's non obviou

This gets me every single time. I also have seen plenty of screens where buttons are given a "selected" state (e.g. a dark blue background), but it's non obvious if the dark blue background means selected or not. Radio buttons and checkboxes never give me these problems. Just use them.