To me its very instantaneously purple, I associate green with acid/corrosive.

Tough i can see that poison->snakes->green (lets just forget about venomous)

Plus, green is generally healing or stamina...

Now the eletricity thing, I never undesrstood from where the hell yellow color for electricity came from (I dont think pikachu was the first, but it definetly set a trend)

Every visible electricity is blue, except for some peculiar photos with peculiar light conditions where its so shiny and kinda explosive...I prefer blue....but games tend to pick any color left for theyr lightning atks...

There are many shades of green, as most people's eyes are most sensitive to the range. There are several sickly-green colors I associate with poison clouds. There are also healthy-green colors. People's faces turn pale and slightly green before vomiting, which is the shade I associate with poisons. I prefer purple clouds for spell effects.

Yellow has been associated with lightning for ages, far before Pikachu. It goes back at least to the dawn of photography in the 1800s since early B&W film was brown/yellow, and in early color film lightning tended to appear as a brown/yellow even though typically it is broad-spectrum white (but can appear many colors).

I don't recall any ancient or medieval art depicting lightning, and Google is not showing me any, but it is likely to exist. I'm curious what colors (or lack of colors) would be used to show lightning in ages past.

I'm used to RPGs where the standard colour scheme is:

• 
  
• Red is HP. Red potions heal (occasionally green can be used for healing too but it can get confused because...)
• Green is venom/poison (also green potions heal venom/poison)
• Blue is MP
• Purple is Lightning, also yellow may be used instead.

Googling lightning really gives 50/50 blue purple pictures...I have never saw purple lightning myself

Unless Poison and Electricity are the only things in your game, I'd try to take into account the entire set of colors, to make sure they all go well together.

For example, if Earth was Yellow or Brown or Grey, but now you make Electricity blue or purple, it'd be more visually pleasing to make Earth closer to an Orange color.

And if you have Plant or Wind as green, then Poison would be better off as a different color, but if Shadow is purple, then maybe Poison should be black (from death, and the Skull and Crossbones usage to mark poison).

And speaking of Wind, that's one I don't get! Why is wind always green? I guess "because blue is already taken by water!", but I'd personally prefer a white wind (or a very pale green), if not taken by light. And if taken by light, maybe light should be Yellow.

(If white is taken by Holy, then Holy should become pale Blue, because, uh, IDK why :P)

Which probably also explains why electricity is yellow; even though *lightning* may be a different color, "electricity" is seen almost everyday in the form of a very pale yellow light coming from incandescent light-bulbs (though this is increasingly changing due to fluorescent, halogen, and LED lightbulbs now being (properly) required in the USA for energy efficiency).

I'd suggest laying out your entire spectrum of magic in a circle, and then tweaking the colors to balance for all four:

• Are they easily differentiateable at a glance? Even to people that are partially colorblind? (Differentiate not merely by color, but also by shape and form!)
• Are they intuitive? Would new players be able to guess them without being told? Would they accidentally forget in the heat of battle, because of years of playing other games?
• Are they aesthetically pleasing, and do they complement each other?

Poison is usually clear. So color it like whipping cream heavily mixed with soap, Watered down with water. And then allow it to sit.

Blue would be weird to me for electricity, unless it's glowing. Yellow is the standard, might as well stick with it. Poison is less standard. But either green or purple is fine. Purple might work better depending on usage. For example if you tint the character's hit points (text or health bar) green, that isn't quite as clear if you also have a status like regeneration, while purple is unlikely to be mistaken for regen.

(Honestly, I'd probably go play a couple of popular RPGs, double check what they do, and use nearly the same colors)

I'm currently playing Magicka, and it has purple lightning and yellowish green poison, with bright green associated with the "life" element (which heals living things).