You’ve seen the photos. Those dreamy, airy living rooms where the walls look like a misty morning on the coast. It’s not quite blue, it’s not quite grey—it’s that perfect, elusive "slate-ish" middle ground. So, you grab a tin of what you think is the right Benjamin Moore grey blue colors, slap it on the wall, and suddenly your guest room looks like a giant bottle of Pepto-Bismol-flavored blueberries. Or worse, a cold, depressing hospital wing.
Choosing a blue-grey is notoriously hard because these colors are basically chameleons. They don't just sit there; they react to everything around them.
The Science of the "Dirty Blue"
Most people make the mistake of looking for a "pretty" blue on the swatch. If it looks like a clear, beautiful sky on that little 2-inch piece of cardboard, it is going to be screamingly bright on four walls. To get that sophisticated, "is-it-blue-or-is-it-grey" look, you actually have to pick a color that looks a bit... well, muddy.
Interior designers often call these "dirty blues." They are heavily desaturated. By adding grey (and sometimes a tiny bit of green or red) to the blue base, the color becomes grounded. It stops being a "nursery blue" and starts being a "designer blue."
Light Reflectance Value (LRV) Matters
Before we look at specific shades, you need to understand LRV. It’s a scale from 0 to 100.
- 0 is absolute black.
- 100 is pure white.
If you have a dark hallway with no windows, a color with an LRV of 30 will make it feel like a cave. If you have a south-facing sunroom, that same color might look like a medium-light denim. Most of the "perfect" Benjamin Moore grey blue colors live in the 40 to 60 range. They have enough "body" to not wash out, but enough "lightness" to keep things airy.
The Heavy Hitters: Which Shade Does What?
Honestly, there are hundreds, but only a handful consistently "rank" as the ones people actually love once they’re on the wall.
1. Benjamin Moore Smoke (2122-40)
This is the gold standard. If you want a color that feels like a spa, this is it. It has an LRV of about 56, meaning it reflects more than half the light hitting it. It’s light, but it’s definitely not white.
- The Vibe: Airy, misty, and soft.
- The Trap: In a room with North-facing light (which is naturally blue/cool), Smoke can lean very blue. In a South-facing room, it looks like a perfect, balanced grey-blue.
2. Boothbay Gray (HC-165)
Boothbay is a bit of a powerhouse. It’s darker than Smoke (LRV around 43) and has a more significant "grey" presence. It’s part of the Historical Collection, which usually means the colors are a bit more muted and timeless.
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- The Vibe: Sophisticated and sturdy. It’s a great "whole house" color if you want a bit of mood.
- The Secret: It has a tiny touch of green in the undertone. This prevents it from feeling like an ice cube. It feels "organic."
3. Mount Saint Anne (1565)
This is for people who aren't afraid of a little pigment. It’s a medium-toned shade that feels very "European hotel."
- The Vibe: Darker, richer, and very calming.
- Best Use: Use it in a bedroom or a library. It looks stunning against crisp white trim (like Chantilly Lace) and warm wood floors.
4. Stonington Gray (HC-170) vs. Coventry Gray (HC-169)
These are technically grays, but they are "cool grays," which means they have blue undertones.
- Stonington: Lighter, more neutral. It only looks blue when the sun hits it a certain way or if you have a lot of blue furniture.
- Coventry: A step darker and definitely more "blue" than Stonington. If you want a grey room that feels blue, Coventry is your guy.
Why Your Room Looks "Off"
You’ve picked the color. You’ve checked the LRV. You’ve painted. Why does it still look weird?
It’s your lightbulbs. Honestly.
If you have "Warm White" bulbs (2700K), they are pumping orange light into the room. Blue and orange are opposites. The orange light will "cancel out" the blue in your paint, making it look like a muddy, sickly grey. If you want your blue-grey to actually look blue-grey, you need "Cool White" or "Daylight" bulbs (3000K to 4000K).
It’s your flooring.
If you have bright orange-toned oak floors, your blue paint is going to look way more blue than it did in the store. Again, it’s that orange-blue contrast. The floors are "pushing" the blue out of the paint.
How to Test Without Losing Your Mind
Stop painting little squares on the wall. The existing wall color will bleed through and mess with your eyes.
- Buy Samplize sheets. They’re peel-and-stick sheets made with real paint.
- Move them around. Put one near the window, one in a dark corner.
- Check at 4:00 PM. This is when the "death light" happens. It’s that weird, low-angle afternoon sun that makes colors go crazy. If you still like the color at 4:00 PM, it’s a winner.
Actionable Next Steps
If you are still stuck, start with Benjamin Moore Smoke. It is the most "crowd-pleasing" of the bunch because it hits that 56 LRV sweet spot. If it feels too "baby blue" when you look at the sample, pivot immediately to Boothbay Gray.
Don't buy the gallon until you've seen the sample in your room for at least 24 hours. The way a color looks at 8:00 AM on a Tuesday is totally different from how it looks at 9:00 PM under a lamp. Trust the "dirty" swatches—they are the ones that actually look high-end when the job is done.