Some people complain that it’s hard to distinguish pop-up menus with their wealth of offerings from a plain button with it’s single action. Visually both look identical…but.
The BeOS has a nice preference panel: /boot/beos/preferences/Menu which offers the ability to set the menu fonts and their sizes (somewhat). You’ll also find a „Color Scheme“ entry here which lets you set the background of the menus to a new color (the text will remain drawn in black).
Now for the tip: Adjust this background color in some pleasing way (purists might slightly lighten or darken from the original gray (r=g=b=219), while the more bold will do as I and simply reduce the green value to 29), you always have the option of the „Default“ button to get you back to the original.
Any new programs run after this will have the new looking menus, both pop-up and regular. This will make it very simple to tell buttons from pop ups!