[RMcNeal]

Based on your pictures, that is, in fact, PEX pipe. It is quite flexible, but not nearly as flexible as the braided line you installed. You can see several of the lines are bent to fit where needed in your picture, for example, the blue and red lines near the braided hose you installed. There's no way PVC could do that without being compromised.
Incidentally, the blue lines are cold water and the red are supposed to be hot water lines, at least in my experience with my unit. I have found white lines also, which feed the water to the black tank flush. I haven't been throughout the underbelly and I haven't removed the coroplast, but so far, that is the only white line I've found.