A NUDE bra (close to your skin color) always works under white and light-colored fabrics!
Here's a photo of what NOT to do :)
This fashion don't was posted in the MissusSmartyPants Style Forum here...
There are lots of great posts on this 'white under white' issue...however there's another great tip posted regarding white pants and pocket show-through here.
That's pretty cool idea for those that still want to keep their pockets...I've always suggested you have them cut out!