Logo background colour changes after uploading

Hello

This query was part of another thread, but I have separated it here because it was getting over looked.

My logo has been created for a black background. The logo text colours are yellow and white. I have uploaded a PNG logo with a transparent background. But after the upload the background changes to solid white. I have doubled checked the original logo and it definitely has a transparent background.

I am aware that I can upload my logo on a black background for the homepage (which I have done), and for the rest of the site, which will have a white background, I can upload individual logos appropriate for a white background, on a per page basis.

But that is extra work, that should really be unnecessary. How can I stop the background changing to solid white after uploading?

I look forward to your reply.