I have bought PYREX branded cookwares that claimed to be borosilicate, but are not actually borosilicate.

You can't visually tell borosilicate and soda-lime apart easily. There is no difference in color (the green vs blue difference is because of other impurities). There is no significant different in refractive index. The only reliable test you can do at home is density (soda-lime 2.52, whereas borosilicate ~2.23, unit g/cm^3).

I measured my "borosilicate" cookwares and all of them are in the ~2.5 range. Turns out they just false advertise. A couple "made in China" beakers I got on Amazon turned out to be borosilicate though. Take that however you will.