U2718Q, replacement, M2B102 to M2B103 differences

You should question what do you think that factory calibration is:

Your UltraSharp monitor is factory calibrated at 99.9% sRGB coverage to an accuracy of Delta-E less than 2

Does this mean each values tested agianst reference to be less than 2dE00? Or does this mean a MEAN error less than 2dE00?
What target is that "reference"? Is it sRGB? Is it native gamut but with neutral grey and sRGB-like gamma?

The visual missmatch you see could pass that <2dE if you choose one option or another. Factory calibration advertisement is ambiguous.

Anyway, this statement is false:

As a photographer, I need both monitors to match as closely as possible before I calibrate.

Use RGB gain controls with your favourite calibration software (DisplayCAL with i1DisplayPro or MunkiDisplay) to match whites, then calibrate, make profile and let color management engine of your applications do its work.
If you use macOS make sure to make "single curve matrix" profiles (DisplayCAL) or "matrix" profiles (i1Profiler) because of the severe bugs present in macOS color management engine for desktop and some Apple's apps (it does not handle independent TRC surves very well)

Hi Yumichan, lets not get lost in the real issue. What I do to calibrate, isn't necessarily what you do, so no false statements here.

The issue here is that there is such a huge difference between the same model, which is I think due to the differing firmware, that if you stood these two monitors side by side, like I have, and viewed them in standard mode, factory calibrated, out of the box, you'd be pretty shocked at the difference; the newer model has a definite warm, orange mask applied, almost as strong as the comfort view setting that's available. So I'm not sure in what environment these were calibrated, but no setting changes could resolve the issue - thus my concern over the firmware.

So, proof to the pudding.

What I've done/had to do in this case, at least to use the new monitor out of the box, is I've flashed the older firmware onto the newer monitor - seeing as that seems to be the only firmware available from Dell - now they are almost identical in standard mode. Not sure if the older firmware being the only one available is in anyway implying that the newer firmware has any issues, but getting the older onto the new monitor certainly improved the situation and I now feel I've received a more or less identical monitor.

So, issue resolved to a certain extent.

"Hi Yumichan, lets not get lost in the real issue. What I do to calibrate, isn't necessarily what you do, so no false statements here."

Not knowing what to do with RGB gains in an sRGB screen... talking about "your" calibration (and at the same time using factory calibration)...miraculous firmware while we are talking about some kind of individual factory calibration to "some target"... Good tale.

So let's go back to the points you do not get:

Factory calibration to what target? What kind of less than X error is Dell talking about? Error for each control color? Mean of errors (worst scenario)?

"Factory calibration" is a very ambiguous advertisement so it should not be trusted for practical purposes. It is important that you understand it...that advertisement is meaningless unless further specification. In some worst case "Factory calibration" could be just talking about grey neutrality (greys do not have a different color than white) and gamma... nothing more.
"Factory calibration" means whatever manufacturer A or B or C wants if it is advertised in a so "empty" way.

If you want a visual match of 2 screen of the same model you'll going to need playing with RGB gains: visually (by yourself, with your eyes) or with some measurement device. That's how it works. Google it, learn about it.

None of the moderators on these forums really have any more information then we do about what's going on behind the scenes. They're just here to hold off the consumers. Since January 2018, several users have reported that firmware M2B103 (which was released to fix a green hue issue) has caused more issues for their monitor - the biggest of which is the bungling of the HDR software emulation feature. Dell has not released any statement to the consumers about this issue or any mention of an update to fix it. The moderators have continually run the users through the usual checklist of possible errors or compatibility issues on the user side, when it is obvious that the firmware is the problem. One moderator even suggested returning the monitors for a refund since it did not seem that Dell was going provide customer service to an issue that had been known for 11 months. It wasn't until another user posted a picture of a refurbished monitor running M2B103, that we learned that Dell is updating the firmware on new (supposedly) and refurbished monitors only. Although, another customer mentioned buying a new monitor that still had M2B102. So, for now, you must send in your monitor, let them install firmare M2B103, and have it sent back. Dell has not made an indication about making the firmware public and if they do, it may be any where from now to 12 months, if ever.