Jon,
I think the ideal dropper toolbar should contain only:
1 a stack of swatches, of configurable length (default e.g. 10), each swatch representing a color that was set on anything by any means (just intercept the set_style signal). Each swatch can be right-clicked for a menu which would have the two commands:
-- Copy RGB (hex) -- Copy RGBA (hex)
2 _two_ toggle buttons for the two modes of operation, each with its own tooltip.
This will give maximum functionality and intuitiveness in minimum space.
Also, please fix the warnings in your code:
toolbox.h:45: warning: 'void sp_dropper_copy(GtkWidget*, GtkObject*)' declared `static' but never defined toolbox.h:47: warning: 'void sp_dropper_copy_as_hex(GtkWidget*, GtkObject*)' declared `static' but never defined