not quite perfect in colors

I bought this monitor to operate both as a desktop extension on iMac, as well as a monitor for the PC. Since I put high value on color accuracy for photo editing (Lightroom 4 and Photoshop CS6), I'm not completely satisfied. The monitor is prone to a bit too strong reds. The calibration with Spyder 3 brought only a fast alignment with the iMac 24 ". With manual correction after calibration I am but then quite happy. Perfect it would be only with two identical devices. Maybe then but the next time a Mac Mini iMac instead?
The format (1920 * 1200), the Anschlüsssen (Mini-Display Port) and the appearance (silver), the monitor suits perfectly for iMac.
I would buy it again or put the Mac Mini a second target. A third point deduction will then rounded it 5 stars.
Addendum: After calibration with X-Rite i1Display Pro, I note that the iMac monitor is light yellow and Dell clearly has the better color and contrast. As a reference to different presentation media (Philips 52 ", iPad with Retina) is the Dell now the better monitor. And with the Fujitsu Celsius PC is no color change over the operation on iMac detectable.
Unlike the iMac, the Dell also needs no warm-up phase. He almost immediately the full luminosity.