First, what are those attacks that are like orange and purple lightning (no not Force Storm?)

 

Also, it looked like Kreia used it on the Jedi during the LS story, so how did she kill them?

it is Called Death Field and it is a popular tatic of the Old Sith

I think the greater question now is: Why did she feel she needed to explain everything to them only after they were dead?

 

She used on them the same technique Nihilus used on her - she severed them from the Force, and they died from it.

It uses the same graphics as other attacks, but it's not death field.

I guess that explains why she didn't bother to use it on the Exile, because if it was a "Death Field" that could kill three Jedi from the Council in a blink, then it surely would have made an impression on the PC!

Drain Life is orange

Death Field is purple

 

I love those powers though I'm LS