Try eliminating one factor at a time to come up with the source of the issue:
Switch out just displays (borrow another if necessary): problem persists, it isn't your display.
Switch out just Colorimeter: problem persists, it isn't your measuring device.
Try a vastly different profile setting for WP and if possible, set the software for a Native Gamma. Better, worse?
I don't have another monitor to test. Actually, I did have a Dell laptop but it croaked a month ago (just in time, thanks Dell).
And I'm not going to buy a new colorimeter because the next monitor I buy will have a built-in one.
I tried different profile settings (like sRGB and random profiles on the list), but the problem persists more or less.
The Dell 3007 came with it own ICC profile file, but It won't install for some reason.
I downloaded the Dell OSD software thinking I might try manually dialing in the contrast, WP, and luminance instead of letting the Colormunki ADC engine take control. But the OSD software won't work. That's again Dell.
I tried calibrating the monitor to the "native" WP, but got ugly yellow whites. I don't think the Colormunki software is able to identify what the Dell's native WP is. Don't I need to reset the monitor to the factory default settings first? And how can I do that when there's no control buttons on the monitor and no functioning OSD panel?
The upside to the story is I experimented with calibrating the monitor to 5500K instead of the standard 6500K, and photos now look more colorful and pleasing to the eye. So I'll set the 5500K ICC profile as default. And move on with my life.