Ideally, I'd get a pure grey (just a mix of pure white and pure black) with an LRV of around 68.
First thing is you can buy a spectrally balanced gray from GTI. Munsell N8 will be closest to your specification of an LRV of around 68.
In regular paint brands there is no such thing as pure black colorant. Each brand's black has a discernible hue bias. Might be bluish, might be bluish-greenish. Same with the white base, there's a pitch of hue bias.
Do they make such a thing?
No.
Every color - including whites and grays - belong to a hue family. It has nothing to do with undertones.
The colors we categorize as gray are child colors that have hue parents. Thus a hue family. It looks like this. Colors of gray are simply the progression of hue parents grayed down in steps
Considering the number of paint chips you've collected, I'm sure you've read all the blogs and comments from people professing that they have indeed found "just gray". They haven't. It's just they found a color that meets their expectation of "just gray" and looks "just gray" in the inherent quality of light they have to work with so they think they've found "just gray".
In order to determine which paint colors are closest to a "pure gray", you have to define it first. And the only way to do that is with data. CIE L*ab values to be precise.
The way you're defining pure gray, it will have an LRV of 68 which means a lightness value of 86. (L* = 86) And you want as little discernible hue as possible. (a = 0, b = 0)
Here are those results. You can get Dulux and ICI The Master Palette colors at The Home Depot.
Whether these options meet your expectation of "pure gray" - in your space - is something only you can decide.
These colors are the closest to L*=86, a=0, b=0 available in major paint brands and they're listed in order of best match. So, Snowfield is the closest.
And, yes, they all still belong to a hue family. For example, Graytint belongs to the Green hue family.
Q
revere pweter white dove
Q