Setting app icons used in taskbar or dock? Many are blank or default
 

Many of the apps I use appear in the system tray as default icons, just blank squares. I run a number of apps at once so there is no room for the text application name. I also switch between applications very frequently, often every few minutes, so this can be a real problem.

This happens in both lxde with lxpanel and with gnome-panel. I haven't tried with others yet. I am able to set the icons shown in the menu, just not the dock or taskbar or system tray (just what IS it called anyway?)

Thank you!