Replacing Torsion Bars

When bars are new - I can see there wouldn't be an issue - but I have a used set and want to make sure I install them front/back as they were on the car they came from ("memory" in spring rate ?)- have no idea which end is front/back since they were painted. I do know that the factory blue mark is on the rear half of the right (passenger) bar when I've seen them.