Being able to change the color of the focus indicator, or have it automatically change based on the colors would make experience builder more accessible. Right now, it depends on the theme, but if you have the background of an app be black, and the primary color as black, the focus indicator is also black and blends in. Have this choice at the page level, widget level, or more customizable at the app level would be very helpful. I attached a picture of a focus indicator around a button on one of my apps.