Wilt Pruf/Wilt Stop and Blue Spruce

On the Wilt Pruf and Wilt Stop labels it says that they may "temporarily" change the color of blue spruce to green.  What does that mean, exactly?  Will the original blue color come back as the product wears off, or it is just a matter of the new growth on the tips of the branches having the original color?  I have some blue spruce and juniper transplants that I want to protect this year, but I don't want to do longterm damage.