Of course you can't!
Hide in Plain Sight is nice, but it doesn't allow you to hide from someone who has Darkvision.
Why?
Because in order to Hide, two conditions must be met:
1. You must not be observed.
2. You must have Cover or Concealment.
Hide in Plain Sight makes it so that you do not have to meet the first condition, specifically: "... can use the Hide skill even while being observed. As long as he is within 10 feet of some sort of shadow, an assassin can hide himself from view in the open without having anything to actually hide behind."
So, you can ignore the first condition, and so long as you are within 10 feet of shadow, you can hide without Cover - which therefore requires that you are using the shadows for concealment.
Given that, how does this interact with Darkvision (or True Seeing)?
"Characters with darkvision (dwarves and half-orcs) can see lit areas normally as well as dark areas within 60 feet. A creature can’t hide within 60 feet of a character with darkvision unless it is invisible or has cover."
In other words, shadows don't exist within 60 feet of a character with darkvision.
The Shadow Dancer or Assassin wraps, from the perception of the dwarf, nothing around themselves, and stands in the middle of a hallway.
The SD or Asn fades from the sight of the human standing next to the dwarf, but is still plainly visible to the dwarf, for whom there are no shadows.
Likewise, you could make a Hide Check in the area of shadowy illumination 35' feet from a torch, and Hide successfully from the human, but you'd stand out like a sore thumb to the dwarf.