It's by design. we're removing the background color for votes.
EDIT: to clarify, I'm only removing the bigger vote boxes' bgcolor, not the smaller vote boxes on the user profile page. Once the latest change is deployed it should look like this:
The bgcolor is removed on the bigger vote box because it doesn't add anything of value, except for cluttering up the homepage and question listing pages. But the smaller boxes should have a bgcolor since it adds more definition to the layout.