there's a side-effect which is surprising but kinda pleasing: the colors in all my games are now WAY brighter and poppy. The colors on the computer itself, webpages, etc. are unaffected; it's just games that are changed.
I want to start by saying I have no experience with nVidia hardware, so I can't point to exactly what's happening, assuming that would be possible in the 1st place. That disclaimor out of the way, there are only a few ways that your display can change.
1) LCD panels themselves are limited in the colors they can display, so PC monitors & TVs etc. use electronics to overcome that. Using the display's buttons & menus many allow some degree of settings like individual RGB levels, and most all nowadays I think offer different modes, which are like presets that change all the settings at once, to for example provide what the manufacturer thinks is a better viewing experience when watching movies or working on docs or gaming.
Some monitors allow software to change those modes &/or settings. I don't know if nVidia driver software is capable of that.
2) Since the 90s there has been concern that what you see is not always what you get when it comes to colors on PC monitors -- the same problem was always there with TVs, but few depended on TVs for anything where colors mattered. Today this means you deal with various profiles that can change what you see on screen, what you see when you print etc.
Many printers & monitors come with a generic icm profile, & you can create a crude display profile using Windows built-in monitor calibration. From there it's kind of a mess -- maybe why Asus for example stopped offering those generic profiles for at least some of their monitors. Windows can be set to use a monitor icm profile, or not, or may use some other profile, even one from a monitor you no longer have attached [see Color Management in Control Panel]. Seperately software may follow Windows' lead, or use profiles or not regardless, or use them to a greater or lesser extent than Windows.
Maybe ironically a more correct display calibration can often be less striking, maybe a bit dull in comparison to more vivid display settings that are often the monitor's default. Graphics hardware drivers can turn a monitor icm profile that you were using off, either all of the time, or just when it detects you're playing video or gaming.
3) Since what you see on screen depends on what the graphics hardware sends the display, those drivers have a huge amount of sway in how what you see is altered, or not. Monitor & TV manufacturers tend to use more vivid settings as their default, so their products might stand out, or at least not look worse than their competition when you see rows of displays showing a demo in stores. For the same reason AMD & nVidia use default settings for video & games that both make things look more striking or vivid, & hide their weakest points -- they want you bragging & showing off to friends how great video looks with your new video card.
AMD & nVidia drivers both have their weak points. There are lots of complaints that nVidia color settings are turned off when Windows starts, & because unpatched, drivers limit the color range to monitors connected via HDMI.
So... I'd think that turning off 3D could have allowed gaming settings in the drivers to take effect -- there's only so much any graphics hardware can do at once, so enabling 3D likely turns other stuff off. Those settings might include changing the colors displayed, &/or they could take control away from Windows using an icm profile, or since it's no longer trying to talk to a 3D monitor, it *might* be telling the monitor itself how to behave.
You could display the monitor's menu using it's buttons to see what you're set at normally, then do the same with a game running. You could check the settings in Color Management & see what it looks like with/without icm in normal Windows. Just after Windows starts you could try enabling the color settings in the nVidia drivers. And you could check out any gaming, color-related settings in the drivers.
If you figure it out then you might enable those settings in part or in full all the time if you wanted to -- unless what you're doing requires a lot of color accuracy, there's no reason your display shouldn't make you as happy as possible. :)
[The maybe weakest point with LCD panels is their tendency to make everything near white, white, & everything near black, black. Part of that is due to the type of panel. Out of the average panels most consumers buy, TN panels are the worst in that regard, but also the fastest for gaming. IPS panels are better, but slower, & the electronic's to overcome that slowness may introduce display artifacts. VA panels may be best, but they're also rare because they can be the slowest.
With the monitor's brightness & contrast settings you can adjust a monitor to display closer to the full range between black & white that it's capable of, with the regretable side effect that it often makes what you see look more dull. How much that matters depends on what you're looking at, your eyes, the room lighting, & your personal preferances -- not everyone notices or minds if blacks get "crushed" a bit.
The only real cure, or the closest you can come to a cure AFAIK is to calibrate the monitor [every individual panel has its own characteristics], using either more involved software &/or hardware. The normal settings on most monitors -- brightness, contrast, & individual RGB levels -- effect everything, no matter how bright or dark, no matter the colors. When you calibrate a monitor you make those same adjustments, only over a range of brightness levels & colors, which is saved to a profile. Using that profile, software including Windows then alters the picture you see on screen, compensating over the entire range of light to dark for what that particular display will show you.
Most people won't bother & that's fine. OTOH it can be worth it. My wife was happy with a new Acer IPS display, I used hardware calibration [a puck measures what a monitor actually displays to generate a compensating profile], & happy changed to thrilled. It now displays almost 100% of the std. RGB color range or spectrum, so she sees new detail in the shadows of her games, yet it has Very close to the same "pop" as the monitor did out of the box at its more vivid factory setting.]
