[URL] It has a green tint by definition Your macbook or iMac is P3 D65 (P3 gamut, D65 white, sRGB TRC), not DCI-P3. Also macOS is color managed (in a simple & limited way) so as I said above: Standard / 6500K OSD preset in your Dell with built in native gamut ICC profile created by macOS when you plugged the monitor should give you what you ask.  
I just got a new Dell monitor today especially for the 98% DCI P3 color to use it with my Mac. When I use the DCI P3 color space my monitor gets a green tint. I was reading some posts and people have mentioned choose 6500K in color and DCI P3 in the color space. If I do this on the monitor settings these are mutually exclusive settings. When I use the P3 color space my monitor gets a green tint.  It's quite disappointing to have a monitor that everyone raves about to have such issue. Any help is appreciated.
U2723QE, DCI P3 color space green tint