Android Question transparent .png bitmaps don't seem to work

I am using bitmaps as icons which I load into labels that sit on a panel which may change colour programmatically.

However when I use .png files they background is always white.
The only way I could find around this is to re-save the bitmap files as .gif files.

Are transparent .png files supposed to work?

I am posting this incase anyone else runs into the same problem.