Standard Gray Neutral 7 Vinyl LatexStandard Gray Neutral 7 is a water-reducible vinyl latex for use in color viewing areas which require Munsell N7/ gray surround as specified by ASTM D1729-2009. Available in gallons or pints.
I'd just take a 18% gray card into the paint dealer and let them color-match it with their analyzer.
I think this would be much too dark. I would definitely NOT want a room painted in 18% grey.
It's fine.