DIAGNOSIS You probably didn't get a bad one. Out of the box, it's set to use a wide color gamut (DCI-P3) but your computer is likely sending a standard sRGB signal, causing a mismatch and oversaturated or weird-looking colors.
FIX You need to set the monitor to the correct picture mode. Press the joystick, go to Picture > Picture Mode. Try sRGB first—this locks the color settings but gives accurate standard colors. If you want more control, choose Custom and then go into Picture Adjust > Color Adjust > Color Gamut and set it to sRGB. That should fix the washed-out or oversaturated look immediately.
IF THAT DIDN'T WORK Check your computer's display settings. On Windows, right-click the desktop, go to Display settings > Advanced display settings > Display adapter properties. On the Color Management tab, make sure sRGB is set as the default profile.
HEADS UP The HDR mode on this monitor (Picture > HDR Effect) can also make SDR content look strange. Leave that off unless you're specifically watching HDR video.