It should be avoided. Without water in the pump it can spin up too fast, causes damage to the bearings and impellers.
Also, while I do not use Feser One UV Blue, I have run across a few cases of people describing gunk build up from the blue.
One of the more famous builders:
http://www.xtremesystems.org/forums/...&postcount=634
take a look at her water block.... does it look familiar. In this case she wasn't using premixed Feser One I believe, but she dye bombed it. It has some tissue residue associated with it as it appears.
Generally speaking, dye coolants are troublesome, and keeping debris from your loops is very important.