Hello R_Giskard, did you find a solution?
I have the same problem and I did a lot of research to solve it with no success.
I recently bought a Dell U2713HM Monitor and plugged it on my Dell Studio XPS M1640 (Mid 2010) laptop, which runs on Windows 7 64 bits. This laptop has a RGBled screen.
I calibrated both screens (laptop and external) using a Spyder 3 elite device.
Strangely, when I look at photo open in Adobe Lightroom 5 or Photoshop CS6 and I move it between the two screens, it appears way more saturated on the U2713HM Monitor. For example, the skin tone on a person is overly orange.
What is striking, is that when I move the LightRoom window from a screen to another, the color saturation only changes when I drop the window, i.e. if I move if from the laptop screen (where colors are paler) to the U2713HM Monitor, the colors remain pale on the external monitor until I let go of the mouse.
It's as if a different color profile was applied to the picture as soon as it "lands" on the other screen.
The change occurs similarly one way or another.
I found the beginning of an answer here: Re: Colors don't match on two calibrated monitors in Lightroom
It has to do with color profiles (in Windows). If you remove all profiles, there is no more difference between screens but you lose the calibration. Still searching for the final answer.