Same here, looks like Stardock won't give a fuck about the customers issues.

In testing here we have been totally unable to reproduce any white flashes that are being caused by the installation of Decor8.  On alt-f4 close the app animates away and on drag from the top of the screen to the bottom the start menu animates in.

Could you perhaps also have other products installed like ModernMix or Start8?

Also I assume your Decor8 colour scheme doesn't have white as the background colour?

I had this problem as well.  I fixed it by clicking on the "clear all" button on the backgrounds tab in Decor8, and then re-selecting my desktop background.  I have to do this every time I restart my computer, but it's a lot better than having to look at the built-in Windows 8 start screen backgrounds.