I'm glad I can help!
Yes, plastic wrap over a cylindrical jar is totally fine, if you have any I suggest you secure it with a rubber band. Actually, you're not supposed to have to do five recrystallizations to get pure spice. After two I generally have some extremely pure and white crystals. Just try to do them both with care and you should get it too!
It depends on what it contains (if it differ). If the yellow stuff is oils and impurities from the solution you pull from, then it should be a little less potent, harder to handle and a bit nastier to vaporise.
If the origin of the colour on the other hand is the amine oxide (DMT N-Oxide), then the effects are a bit different but not the potency (as much). N-Oxide in it self is psychoactive and considered by many as a more gentle, guided and slowed down version of DMT (at least if it's only present in small amounts). It is actually prefered by many to have a little yellow crystals if this is the case, so try vaporising it.
I prefer to make really pure crystals, and then oxidize these to my favourite amount of light yellow tan. That way I know that the crystals are impure with the N-Oxide and not oils, I have control over the amount and I can have the option enjoy pure white (if I only oxidize parts of it) if I want to!
There's a clear difference between what I say I do and what I actually do perform.