Slate Blue
Slate blue is a blue with a substantial quantity of grey in it, and its character comes from what makes up that grey. A slate blue greyed with black turns cold and flat; one greyed with a little earth or umber stays soft and keeps some depth in shadow. The difference is invisible on a small sample and obvious across a whole wall.
The tone comes out of the working parts of old buildings rather than their reception rooms. It appears on shutters, sash frames, dressers, panelled passages and painted floors, where a colour was wanted that would not show wear and would sit quietly behind whatever was placed against it. That background quality is still its main use.
Because it is close in value to many woods, slate blue can make joinery disappear. That is useful when a room has more panelling, doors and cupboard fronts than it can comfortably show off, and unhelpful when a single good piece of joinery is the point of the room. Test the colour directly beside the wood before committing to it.
It takes white trim badly and off-white trim well. Against a bright white the blue looks chalky and slightly cheap; against a warm stone or bone white it looks considered.