Cairo / Highlighting

[Sebastian Geiger <sbastig gmx net>]

Hi,

given cairo type cr which contains an icon. How can I produce some kind 
of highlighting on this icon. For example light it up a little and 
change the background (the parts which are transparent) to a different 
color (e.g white), or even using a light white blur as background.

Im sure it only requires a few calls to cairo but as I am not very 
familiar with cairo maybe someone can give me a suggestion.

Best Regarads
Lanoxx