Xtol will remain clear whether you pre-rinse the film or not. I haven't tried all films with it, but in my experience there is one exception: Foma 100, 200, and 400 films. The sensitizing dye of those films (in 120 format) will actually tint the developer a stunning turquoise color that's really attractive!
Since I stopped using those films due to some nagging quality problems, my replenished solution is increasingly losing its turquoise tint. I'm almost sad to see the color go.
Now I use Kodak Tmax 400/100 and an odd roll of Acros. I don't usually pre-soak the film, but did once to see if I could tell a difference in the negatives. The water rinse came out a deep deep purple from the Tmax 400 films. But the resulting negatives looked, scanned, and printed the same as always.
So don't worry about it. Clear Xtol is normal.
- Thomas