What has that got to do with guidelines? The color bands appear on non metro tiles irrespective of the application.
You are not understanding the problem. Not a show stopper bug but definitely annoying.
The Desktop app tiles on the Start screen will be re-done for RTM. A recent demo from Microsoft last month revealed the same - the icon will be larger and centered, text will go down, unlike the current style which is pretty ugly and thankfully temporary. Also, pretty much consistent with the Metro tiles though of course Desktop tiles will be static.
A more pressing issue with Metro UI is the lack of ClearType. Some might argue that there will be a whole generation of high-DPI devices Windows 8 is designed for, and that is definitely correct. But most laptops in 2012 and before still use 1366x768 - definitely not dense enough to hide aliasing.
And yes, Search is brilliant but it can do with an "All Results" tab. IIRC, this was there for DP. Now that there are no crippling real estate limitations, All Results should certainly be an option, if not default.
I am sure these will be fixed by RTM time.