ok so I used to be able to do this on photoshop and save a pic to keep its transparency so the background color would match any website color

for example see my sig

the background color around the photo's shadow I had to screen shot d2jsp after a post and use the eyedropper tool to match the color

but the color is different on my profile so the difference is noticeable

what file type when saving in gimp will support transparency? .jpg isnt allowing it when photoshop did and requires me to flatten the image and then it adds a background color. How do I avoid this in gimp??

I use PNG in Gimp all the time, try that one out, also check if when u hide all but the background, is it the cubes of transparency or white?

GIF, PNG, BMP, TIFF