I've gone to the DD walkthrough at Banshee (only one I know of) and they listed everything in the game it seemed like except potions. Or I couldn't find them. Does anyone have a link explaining ALL potions/drinks in DD??? I already know all the affects from most of the "plain" drinks as the Banshee site does list all of those, and I already understand red, blue, yellow, green, black, orange, white potions and purple elixers but not a single glass of stuff I got called Purple Potion and I couldn't find anything for the Superdrug (I thought it would cure the plague, but nope, that didn't work, and when I took it it looked like it raised some resistances and lowered others or something because I had one in negative territory.

Purple potion (as opposed to the purple elixers, which I already know too) appears to only regenerate 21 hit points unless I've missed something there.

And the mysterious black crap you get when you help the cook in the castle appears to me to just be a shadows potion, anyone have more detailed info??

And finally, regarding the shadows potions, what affects when you become visible again? Because sometimes I swear it seemed like I would here the "I'm becoming visible again" warning within seconds of taking the darn thing.

Check out the Locus Inn Alchemy Guide or the Larian forum topic Alchemy Spoiler Thread.

Superdrug potions give a temporary (though it lasts quite awhile) -100 spiritual resistance and +100 poison resistance. You need some unique cure potions to help the plague victims (check your quest log for additional hints).

That small amount of healing is all purple potions do, and the strange spice is just a shadow potion.

I only tried a couple shadow potions, but AFAIK using a lever or opening a door, etc, direct attacks on opponents or getting too close to a light source will make you visible before the time limit runs out.