You can get the pex in different colors for hot and cold. If you are replacing it all you might want to look at adding a hotwater heater bypass system to make winterizing easier. Basically you add a valve close to the hotwater heater on the line in and the line out. Then add a connector line with a valve in the middle of it between the line in and the line out. The 2 valves on the lines in and out will be closer to the hotwater heater than the connector line. During normal operation the connector line valve is closed and the other 2 are open. When you want to winterize you close off the 2 valves close to the hotwater heater and open the valve in the connector/bypass. This keeps the antifreeze out of the hotwater heater.