Custom icons for MS toolbars?

MS Office products (Word, Excel, Outlook, etc.) allow you to customize the toolbars by adding your own icons. It even gives you an icon editor. But the built-in icons look like they are at least 256 colors, whereas the icon editor gives you only 16 colors. There doesn’t seem to be any way to create custom colors (like when you select a background color in the application) or to import an .ico file to use for a toolbar icon.

Unless I am missing something that the Teeming Millions know about.

Is there any way to create your own icons for toolbars that are better than 16-color ones?

Not even a guess?