Model number please.  

BIOS (F2) > BIOS > Display > Eco power save (should be off)  

Thank you for the response. XPS 13 9310. I have no option for that under display in my bios. I only have brightness on battery/AC, whether or not touchscreen is enabled, and "full screen logo." I also used the search feature in the bios and could not find anything close to eco power save.

Yes I checked it myself, options is missing for some Dell models. 

Since 13 inch model comes only with onboard graphic (intel) need to look in that. 

Have you tried 
Intel Graphic Command center (you can install it from store) 

Enhanced  power saving Turn it Off 

Display power saving : Turn it off. 

Thank you again. Yes, I have both of those turned off.

Thank you! Reinstalling the graphics driver solved my problem.

As for your other suggestions, just in case you were wondering:

I have an option to adjust brightness, but it doesn't really do much as it relates to this problem. In power options their is no option for adaptive brightness. I also looked at the link you sent and none of their suggested solutions are applicable to my laptop (it seems outdated). Thanks again!

This did not solve this problem for me and the other one of removing the driver does until the driver is reinstalled. I have found the solution though. Part of the Intel Iris Xe Graphics software is a tool called 'Intel Graphics Command Center'. Open this app, then click the 'Display' button on the left tabs, then on the General tab scroll down till you see 'Local Adaptive Contrast Enhancement' and turn this off. This is an independent tool from the windows screen brightness and as far as I can tell has to be done from here.

I had this problem on my XPS 13 9310 too - in bright sunlight the greys were all getting washed out and it made some text unreadable. I solved it in the Intel Graphics Command Center by disabling the option, "Local adaptive contrast enhancement" under the Display tab.

I cannot find this option anywhere in the program or in my system. It seems it has been removed from the advanced power options, the BIOS options and the Graphics Command Centre. My model is XPS 15 7590 and I have been trying to disable the greying out of whites as it drives me insane while photo editing or watching movies.

Hello Adomas!

It's quite possible that you solved this issue by now but I just aquired a second hand XPS 13 9310 and I was having the same problem. This is what I did to solve it:

1. Download DDU from here.
2. Disable my internet connecton momentarily.
3. Boot in safe mode.
4. Uninstall the driver from there using DDU.
5. Reinstall the Intel Driver appropiate for my device.
6. Download and install Intel Graphics Command Center Application. I downloaded this version.

Now I have Contrast Enhancement option available but it's off by default 👌

Edit: I've just realised that's not the same opinion that people mentioned in the thread but, for whatever reason, after reinstalling the driver, the problem is gone. And I still don't have the "Local adaptive contrast enhancement" option.