OK so here are some more photo's Also must correct an error the 27" Apple Cinema actually supports up to 2560 by 1440 pixels, which is why I guess it seems fine for 4 K video
Sorry about the room reflections these were quick iPhone 10 photos and are untouched
So again. the Cinema on left the 5K iMac on right
as you can see the color is slightly different but fairly close (the Cinema seems to have a bit more blueish cast in the white),,,, the 5k is just a bit brighter and a tiche sharper
Cinema
iMac