I have always used a PG base with my nic. Early on, I remember reading in other forums where nic in VG bases had a slight pinkish hue and those in PG had a golden hue (and vice versa!) when exposed to oxygen.
My thoughts are... the nic is probably just fine. I wouldn't be that concerned with the color just yet. Heck, I have +/- year and a half old nic (freezer stored) that's a deep golden color; it still titrates out to 100mg/ml with no problem and has no off taste at 6 to 9mg/ml in my mixes (VapersTek/Chemnovatic nicotine).
Please do! I know we all WANT to trust the folks who sell us our product... however, everyone can have a bad day at work and screw the pooch; it can happen to anyone... including at companies that package/bottle our flavors and nicotine. There have been a number of Reddit shit storms in the past over this issue!
Protect yourself and get a titration kit... test your nic for accuracy... peace of mind is a good thing.
I can tell you for a fact... people have received nicotine from certain vendors which titrated out close to 180mg/ml, when the concentration was supposed to be 100mg/ml. It's happened before and will probably happen again.
It's a long thread read... 2012 til today, but you can glean a lot of good info out of this thread below... you can also use the word search feature to get yourself closer to specific posts.