Eddie kindly praised the avatar I have. Thanks, but it only took me a couple minutes to get rid of the white box I saw.

I used GIMP. I made a new 100x100 image. I set a gradient with the "deep sea" option in the gradient dialog. I chose a true type font called "denmark" for the character.

I already have some V avatars but couldn't find them on the laptop. So I chose a big plain white question mark. I rotated it and enlarged it a little. I chose to alpha selection (tilted question mark), added a new layer, enlarged the new layer's selection 2 pixels, filled with black, and ran a Gaussian blur at 10x. Lowered that layer beneath the original white question mark to give it a bit of shadow against the background. Reduced the opacity of the shadow layer a little (just until it looked "right" -- I don't remember how transparent I made it).

Easy. And no more white box.