RV Repair: dark patch appeared on vinyl flooring., vinyl flooring, palomino

Question
What is it?  When we took out our trailer (after the winter),a 2006 Thoroughbred(275)by Palomino, we noticed an area (about 6" X 4") on our vinyl flooring in the living area that is dark, I tried washing it but think it might be underneath. It is mold? It's grayish/greenish. I thought that it might of been from our pull out rubbing on the floor or maybe something leaking from underneath the pull out onto the floor.  But that seems unlikely.  We really don't know what caused this patch. How hard (or expensive) would it be to change the vinyl flooring if need be. Can we do it ourselves, if so, how?  Thank you so much in advance for helping us figure this out.  Much appreciated!

Answer
Barbara, This is probably coming up from underneath. To change the vinyl I would have a professional do it as there are always things they know that you don't, such as whether they can glue to what you have or not. I would first try to locate the trouble to make sure it doesn't happen to the new floor. Thanks, Bill