Some common pine lumber is red naturally, if it is treated it may stay red. I know of no treatment so far producing red color. If it is 15% treated wood it won't last long. If it is 40% treated wood it should compete with natural red wood. Problem is using redwood as planking for walk decks is the modules of lasticity and fiber bending properties of natural redwood. Suspect spanning capabilities will force you into treated wood. Treated wood should serve you fine if not in direct contact with dirt. I feel natural redwood will last longer concerning rot. However not sure natural redwood will serve you well laying flat as walking platform planking for a floor, probably will bend and not strong enoungh installed in that manner.
Just my opinion