As they have explained on their site, you cannot print white! There is no standard white colored ink you can use in your regular desktop laserjet or inkjet printer. Without the white as a base any light colored decals you put onto a dark background tend to disappear. You can see an example of this 'fail' on my Scythe's Commanders backpack banner. The strong yellow became quite faded. You may not have noticed if I didn't admit this. This was a decal I printed out for myself. I didn't create it.
If you have ever worked with decals, you may notice that may of the bright colored decals have a white background when you look at the backside. In painting terms, think of this as the base color before the main layer goes down. It gives the light color something to build off of when placed onto the dark colors.
Why am I excited for this? Because the decals I have for my Scythes are a perfect candidate for this upgrade! Here are the decals from the Bell of Lost Souls site. I also created a sheet of generic unit designations too. These would be great in white!
You don't have to recreate the pyramids to take advantage of this opportunity. The decals on the Bell of Lost Souls site are free. You can grab some of the BOLS decal sheets that are in color and have them redone on a white background. It would make it so much easier to build up your Heresy era Space Marines, especially for Ironhands or Raven Guard. Here is a quick link to help you find them faster!
So, hurry now as the Kickstarter ends on the 23rd of July. I am sure you can still order from them afterwards, but I am also sure the cost would be higher.