Thats because it is using the Featured Page/Post widget code and it’s adding the white background and box shadows as if it were being used in the sidebar……that’s something I’ve added to the update list to fix.
In the mean time add this to your css –
.welcome .entry {
box-shadow: none;
-moz-box-shadow: none;
-webkit-box-shadow: none;
background: none;
}