Because blue is a primary color, it cannot be made from other colors and must be produced independently. Lights are often filtered, while paints are mixed from base components.
A white spotlight used with a blue sheet of polycarbonate (known as a lighting gel) gives blue light. A pure blue color on an LCD monitor is given by activating only the blue sub-pixels.
Blue paint is mixed by starting with a pigment, such as lapis lazuli (a mineral), which is first ground and then mixed with a binder, such as tempura or linseed oil, so that it can be spread with a paintbrush.