>>In my treeview, I have several bitmaps. They have a grey background.
>>This
>>is good is the user has defined his Windows configuration to use grey
>>background. For those user having a Windows configuration with a white
>>background, I can see that the bitmap is not transparent. Do we have
>>to use
>>a mask to avoid that problem?
>
>Have you tried setting the 'transparent' portion of the bitmap to
>white?

Thanks, putting white in the background does the job.