First of all, that bug should be fixed.

> On Win32, in the 3-button mapping, the middle button is mapped to
> "blue", but at the Squeak level it will appear as a "yellow" button.

Which is a result of the bug - the code looks correct. The other platforms
need to be updated to actually use the defines.

> 	red  =>  main, primary
> 	yellow  =>  menu
> 	blue  =>  halo, gesture

I'd leave the colors in the code. If you need to explain what these do: 

	red    = primary
 	yellow = secondary
	blue   = meta 

For mapping to physical buttons, primary & secondary works fine for left &
right buttons. And with modifiers, Meta/Alt/Cmd+primary = blue is also
self explaining. The third button is hidden under the wheel anyway
nowadays.

-- Bert