The border. It would look better if it was black. This signature mainly consists of darker colors. White borders really only work with signatures that are very vibrant and have a lot of light colors. Not only that, but the border is too thick, and thick borders like the ones this signature has can tend to be a bit distracting.
I assume you use the stroke-style of border? Try putting it on Inside at 1 px; that seems to work the best.
Hmm.. I tried changing the border to many different variations but to be honest I didn't like how it looked like with a black one. I personally like thick borders a lot. It feels like they add something extra to the sig.