I don't know how exactly to describe it verbally, but I just mean the white triangular arrows in this example image:

In an icon theme that I'm trying to use they either don't exist or are the exact same color as the menus that they're on top of. I don't know how to look up what their standard filename is in GNOME/GTK/whatever icon sets because I also have no idea what they're called in a general sense. I just want to go into that theme's folder in /usr/share/icons and either put them there or replace them with ones that are actually visible.