The (non-torsion-type) springs on my garage door have never been
replaced since I bought the house about 25 years ago. I'd like to
replace them before I'm forced to.

In looking around the net it appears that springs these days are color
coded on the ends and that people replace the springs with ones with
the same color code. Mine have no color code - maybe the codes didn't
come about until more recently, or maybe it's rusted off... so how can
I determine the proper springs?