It does eventually. Most of the manufacturers of spray finishes, such as pre-catalysed lacquer, acid-cat lacquer, cellulose polish, etc, state something like a two year or so shelf life, which gives them decent leeway before the stuff becomes really unusable. I've successfully sprayed lacquer four or five years old, but that's followed a test application or two to be sure the stuff's still good.
If what you've got isn't going on as it should, and the colour has changed, it suggests to me it might be beyond its usable date. How old is the polish? I'd get new stuff, because generally the cost of a bit of polish is not really large compared to the effort and time put into a project. Old paint and polish and other chemicals with VOC's can usually be disposed of properly at council dumps nowadays, but check with them for their policy. Slainte.
