What does blue and green make?

1the mix

Let's mix two colors, blue and green, and see what shows up depending on whether we're using light or paint.

2light: additive

With light — like on a screen — colors ADD together. Blue light plus green light makes cyan, a bright blue-green glow.

3paint: subtractive

With paint or ink, colors SUBTRACT light instead. Blue paint plus green paint gives a duller, darker teal — not brighter, because pigments soak up more light the more you mix.

4the rule

So the rule is: on a screen, blue and green light stack up brighter into cyan. On a canvas, blue and green pigment blend down darker into teal.