It would indeed be nice if you could "style" an API zone like any other layout area. But it's actually not too hard to fill it with a color once you connect to it.
The issue isn’t that filling a zone with color is easy or hard, but that API Zones can live on up to eight different pages with unique indices—and the API gives you no way to know which page a given index belongs to or which page is currently open. Without that context, you can’t reliably target a zone for coloring. A simple toggle in Erae Lab to show or hide the zone boundaries at the hardware level would remove all ambiguity. Erae Lab already includes a style feature where touch displays a ring at the touch location area, so adding a boundary toggle would fit naturally with existing functionality. Alternatively, if the boundary-request response included page numbers and page-switch events were emitted, per-page coloring could work—but the current API doesn’t provide that.
YUKITAKA