Using Image List with Treeview / ListView - transparancy problems

Dear All

I'm having slight difficulties using an Image List with a TListview
component.
I have created a number of bitmaps to appear in the List view and have used
the colour clOlive as the intended 'transparent' colour.  However, when I
associate these images with an Image List and set the transparent colour to
clOlive - any white within the bitmaps is treated as transparent as well??
(Therefore converted to the default Listview colour clWindow).

I have tried various configurations of the Image List properties BkColor,
BlendColor and DrawingStyle but it doesn't affect the result.

Can anyone tell me what I'm doing wrong?

Thanks

A Chapman