Schematic HR diagram: on the right and left of the vertical dashed line the Yellow Void and the Yellow-Blue Void, respectively (data in Table A.1: data summary of the appendix). The diagram shows the extreme physical and photometric values of one or two (HR 8752) selected RL or BL evolutionary tracks of the program stars (arrows). Most of the extreme values are accidentally concentrated near the vertical curve on the right, the curve where H is close to beginning their ionization.