Yea as far as humics, the more yellow it is, the lower molecular weight it is, and basically the 'smaller' it is. Fulvcis are just the lighter ones, so its actually a whole gradient from humics -> fulvics, without really any specification of what is what. The fulvics are smaller and can actually enter plant tissue, help with nutrient transport, help transport immobile nutrients (kinda cool). The heavier humics dont enter the plant, and mostly act as a chelator for metal ions- keeps em from reacting as readily, potentially can help with toxicity too (think of it like time-release metal ions).
Apparently humics are better for microbial life than fulvics- i guess they kinda 'feed' off of the ions that the humics catch, and apparently can consume the fulvics themselves. I guess for soil, you want humic heavy because the benefit to the microbe/rootball area are better, for hydroponics you apparently want fulvics because of the inner-plant activity. Im not sure any of that really makes sense to me, but I'm trying to go as 'fulvic' as possible.
At least all the humics ive seen come from leonardite- which is like a soft coal, oily kinda stuff. There's naturally humics in sea kelp, which is why it makes a great foliar. You can make it even better by using more fulvics and whatever other nutrient source you want, as it'll carry the metal ions into the plant. Sea kelp also has bennies in it (i think mostly Subtilis).
This is why I'm really interested in floralicious+ (even though it destroyed my rez last time), its mostly humics and kelp. And when you add microbial activity, the kelp can be broken down further to release all sorts of hormones into the root zone. So for right now im treating F+ as basically a microbe/tea additive. Kelp isn't useful in hydro until its broken down, so I just do all that during the tea process.
