Dell XPS15 9550 Laptop - No TrueColor(32-Bit) on secondary monitor (2560x1600 Dell3007WFP-HC)

Hi

I have a color problem connecting my XPS15 9550 to a Dell3007WFP-HC as a second Monitor. It works Fine concerning resolution, but on the external Monitor i dont have TrueColor.

Here is the Setup

I cant Control Resolution trough the Settings in the Intell HD-Graphics App (2nd Monitor doesnt show there).

Laptop :    XPS 15 9550 (i7-6700HQ CPU),16GB Ram
OS Windows 10 Pro (64 Bit Version 1607 Build14393.693)
Internal GraphicsCard: Intel HD Graphics 530
Internal Screen with Resolution : 3840x2160, TrueColor(32-Bit),60 Herz

Docking Station D3100
Connected External Monitor
Dell 3007WFP-HC connected trogh KDP70 (Genuine Dell DisplayPort to DVI-D Dual Link Adapter)
GraphicsCard: DisplayLink USB Device (Dell D3100 Dock Driverversion 8.0.762.0)
Resolution 2560x1600 "TrueColor(32-Bit)"??????????? ->not really!  Massive Color Banding!!!,60 Herz

Thanks a lot for Your Help!
Dan