Just got some from a rebottler, and it's Black. Is that normal?
Sounds about right. Mine is a deep chocolate brown. It barely lets the light of a flashlight
through when held behind the bottle. Remember you are using it in very small quantities (0.5-1.0% per vendorsuggestion/ I use 0.25-0.5%) so it shouldn't have much impact on the overall recipe color; at least it doesn't for me.
That's funny! I finally got of my duff and mixed up eight new (to me) recipes that have been clogging up my "want to try" list. One of them was a simple lemon and biscuit (both INW) mix.
In this latest fit of mixing I also have a more complex pear and biscuit recipe that
@MsLoud shared earlier in this thread. While starting to taste these, AND being lazy (I didn't re-wick between flavors

), I think I may have stumbled onto something. I had the lemon/biscuit in a small thank first (on fresh wick), and then moved to the pear/biscuit. (The tank is an Avocado 24 by Geek Vape w/single coil; so the wick has pretty long tails to reach the bottom of the tank.) The lemon biscuit wasn't bad but the lemon was very much faint and in the background (INW at only 1%). I vaped the tank down to where I no longer had any free-flowing juice left in it but did not vape the wick dry (it's a PITA to get it wicking freely again when I do that). I then filled the tank with MsLoud's creation. MAN! Did the lemon pop smack out right in my face!
I don't know if it will help with flavor longevity but it sure made the lemon sing. This is going to require further experimentation.
You would think if these companies can make a flavor like that,that will hold up,that they could make a good straight lemon that would hold up.
The only thing I can think of is that the bulk of the "taste" of a real lemon (the fruit) (aside from the sour created by citric acid) is mostly aromatic. These translate as volatiles in our flavor concentrates. Volatile's, by their very nature of being volatile, readily evaporate at room temp. I believe this is why we experience flavor fade relatively quickly with flavors like lemon; especially when they are stored in permeable plastics or excess headspace. Heat and open-top aging are really no-nos with lemon as this will only accelerate fade. Mix..., shake..., and vape... for maximum enjoyment (for me anyway).
Now as to why flavors like lemonade seem to overcome this fading; I have no clue.

Unless the volatiles are able to bond with something else in the blend that slows the evaporation. But that is only a wild a** guess.
Have you tried a combo of the two to hold the flavor?
I have Lemon Sicily-FA, Lemon-INW, and Lemon (water soluble)-TFA and have played with all three; as single-flavors and a couple of 2 flavor combinations (TFA/INW, and INW/FA). The combos didn't pan out any gold yet but I only tried one iteration of 50/50 for each of them. Fade longevity didn't improve; still about 9 days tops for my taste buds. My take-away: don't mix more than I will likely vape in a week.