NfinAt

Hello Everyone,
This is all a bit new to me, but I must take the time to say hello and partially introduce myself. Female from The South. Took my first vape over 2 years ago and 5 minutes later I threw my cigarettes away and that is my story. Looking for great e-liquid suggestions, meet others, ask questions from others in the "know", but anyway so to have gone on like that. I guess I may have messed up. I was just supposed to say hello.....HELLO EVERYBODY. I am so happy to be here. Thanks.

I'm thinking our resident mixologist @Compenstine might have an idea or two about what's going on with your juices.
In my experience, excessive heat tends to turn some juices a much darker color and can give it an "off" flavor just as Bebop said. I've had some juices that I liked a lot turn into an awful tasting concoction when I accidentally left a small carry bottle of it in the car on a hot day... oops! 
 

My experience is that excessive heat deteriorates juice pretty fast, both in color and taste.  Im sure it varies by juice.  Generally keeping them at room temp or below seems to be ok but even a day or two in a hot car or something is pretty bad. You may have even noticed your juice darkening in a tank from atomizer heat (even more so with sub ohm). 
I haven't looked at any studies but I would think with these food grade flavorings that we do run the risk of it going rancid pretty quick with excessive heat. 

Over time the nicotine oxidizes, which turns dark. The best way to store mixed juice is in the refrigerator. There have been reports that juice kept in the freezer will last for years. As far as what heat does, some people steep their juice with heat, others can tell you about that. I hope this answers your questions.

You didn't mess up at all. Welcome to Vapor Talk.   

Welcome!

Welcome to VT, we are glad to have you join us.