I am impressed with the new Windows Phone 8 startacreen, but there is only one problem! still no customization, we are still left with the boring colors, though I hear more colors are being added.
Thankfully, there is MegaTile, an app that lets you customize your start screen (to some acceptable degree). It currently is available/compatible only for Windows Phone 7 and with the new WP8 startscreen coming soon (this fall), I reckon the publishers of this app should be up on their heels to make sure the they put out an update to make it compatible with WP8.
In the meantime, you can get the MegaTile app from the Marketplace for $0.99 (reasonable price).