I'd hate to think I'd have to edit bitmaps to specifically fit the colours of the background manually everytime! Any ideas?

Do bitmaps really support transparency? I thought that feature was unique to GIF and PNG.

This stickied post points to a neat hack.

you could try to use Red: 78, Green: 111, Blue: 214, that colour seems to be transparant in winntbbu.dll

Sphinx, I tried your suggestion just now, but it seems both XPreview and WinntbbuEd show non-transparent blue bitmaps that clash with my darker background still.

Can these two programs be regarded as reliable?

xpreview does not show this transparancy, but winntbbued should. i've noticed though that winntbbued does not place the text properly... i noticed you had looked at my winntbbu file in the other thread, if you download that file i've posted with that thread, you'll see what blue shade i use, and if you look at the top checkmark in my preview image you'll see that it is transparant. it could be that you're using something that's antialised (fuzzy edges), then that is why you get other blues in the preview, but since i haven't seen your design, it's hard to say.. that is something you'll see in either my preview or if you download the .rar and look at the images in there..

oh yeah. and the Visual Style i use is Clearlooks 0.6 (http://hsn.deviantart.com/)

that trick doesnt work for me