The phrase "a dull blue" is correct and usable in written English.
It can be used to describe a specific shade of blue that is muted or lacking in brightness.
Example: "The walls of the room were painted a dull blue, creating a calm and serene atmosphere."
Alternatives: "a muted blue" or "a subdued blue".
"I'm told that the light was a dull blue light," Mr. Bay said, "kind of like a night light, in Dr. Lee's room and that the jail would use that just to make sure that if someone walked by and looked inside his cell that they could make sure that he was there and that he was doing O.K".
The top half was militia gray, the bottom a dull blue.
When fresh, the surface is reminiscient of jelly or wax, and can be smooth or warty, varying in colour from a dull blue to lilac.
Debruge felt that the opening 40 minutes were "a dull blue-collar drama populated entirely by stereotypes," and while the film "picks up some much-needed momentum" with the actual heist, the "resolution feels rushed".
It has a particularly brilliant blue colour and is very lightfast, but it is not suitable for use outdoors because it weathers to a dull-blue powder.
Instead, it's a uniformly dull blue and white palette with the odd integrated Google map to brighten things up.
If your shoes are a light, maybe dull blue you can still make those suckers pop!
Fair enough – she spends most of her time saving the US so we can forgive a few go-to dull blue or pinstripe suits.
The sea was the dull blue of a cataract, surrounded by small volcanoes, bubbling mud pots, and ragged, blank mountains used for bombing practice by the Navy and the Marines.
And for half an hour we've been on county highways, all straight lines and right angles, cutting through plowed fields of cotton and soybean, seeing no other vehicles, no people, no lights except the distant dull blue of a farmhouse television, and then this explosion of busyness, in this place near no place, an embellished dot on a road map.
The Dead Sea is a dull, pale blue that reminds one of the Great Salt Lake, and the hills across the water that wall it in are of yellows and purples and blues and browns so dull that such words for color are almost too vivid to refer to them.
