Comparing colors on the 2014 and 2019 iMacs
I knew my new iMac had the wide color gamut (P3) display, but until I used it side-by-side with my old iMac, I didn't realize just how different things would look. In my comparison test of the two iMacs, there are a couple of photos of onscreen images—one set with the default iMac color profile, the next with the Adobe RGB (1998) color profile—the differences are quite obvious, especially on the default profiles.
Here's one last image, with a comparison slider, so you can more easily see how the colors change. (Thanks to Kirk McElhearn for the source photo.)