I've been using a modern electronic ballast shop light to test some vintage 48" tubes. Worked fine until I got to a pink GE preheat tube- looked perfect, but wouldn't start. Do I have a bad tube, or the wrong type ballast?

I don't know for sure, but I do know that different tubes can have different voltage cathodes, and lamps designed for one type may or may not start on ballasts designed for another type. I'm not an expert on fluorescents, but I'm guessing old tubes would be designed for switch-start, or preheat as it's known in the US, so they may not like electronic ballasts all that much. But I'm sure someone will be along soon to correct me if I'm wrong (not an unusual occurrence  )

Using older preheat-only lamps on rapid start or electronic ballasts may shorten their life a bit, but they should start up fine.  Most likely the lamp has lost vacuum, or one of the cathodes is broken.  If the latter, it might fire up on an electronic ballast that does not require cathode continuity (assuming yours does).  An RF lamp tester would be useful here.  I typically test lamps with a plasma globe.  If a fluorescent lamp illuminates when held up to the plasma ball, both cathodes have continuity (verified with a multimeter), and it's not blackened at the ends, then the lamp is almost always in good working order.

I've got one of those Martindale testers, they work well, although they really only prove the integrity of the gas fill, they won't tell you what type of cathode a tube has. Older tubes do typically require pre-heating, although I may be wrong, as I said.

Right, though if it illuminates under such a tester, a continuity test confirms the cathodes are intact, and there is no visible darkening, it will almost certainly fire up.  Perhaps mild gas fill contamination or mercury starvation could be present, but it'd probably light up partially at least.  Although driving a preheat-only lamp with HF electronic may cause excess wear, the high voltage will certainly get it going.  Regrettably,  I suspect the lamp has taken in air, though it wouldn't hurt to do some additional testing to be sure.  Some ballasts only require continuity at one end, so reversing it might help if it's that.  Any electronic ballast with shunted sockets won't care about continuity.  But if there's no vacuum or a cathode has broken free of both supports, that's the end of it.