What colors make brown?

Mix red, yellow and blue. Two parts red, two parts yellow and one part blue gives a mid brown. Equal parts of all three, 1 : 1 : 1, gives a very dark brown that is close to black.

The reason is that brown is a dark orange, which is how Wikipedia's article on brown describes it. Red and yellow make orange, and blue, the colour opposite orange, darkens and dulls it. Keep the blue to less than the red or the yellow and the mix stays brown. Let the blue catch up and it heads for grey and black, since paints work by absorbing light and all three primaries together absorb most of it (complementary colours).

Any paint mixed with its complement, the colour opposite it on the painter's colour wheel, comes out brown, grey or nearly black. In the traditional red, yellow and blue model the pairs are red and green, yellow and purple, and blue and orange (Wikipedia).

Each pair is all three primaries in disguise. Green is yellow and blue, so 1 part red to 1 part green is 2 parts red, 1 yellow and 1 blue: a red-leaning brown. 1 part blue to 1 part orange has twice as much blue, so it comes out dark and greyish; 3 parts orange to 1 part blue is the warmer brown most people want. Yellow and purple, 1 : 1, gives an olive brown.

This is the handy route when you have only a few tubes. Brown an orange with a touch of blue, or knock back a green with a little red.

To lighten a brown, add white. A tint is a colour mixed with white, which raises its lightness, and a light brown with plenty of white is a tan: 1 part each of red, yellow and blue to 6 parts white. Yellow lightens too, and warms the brown at the same time, so 2 red, 3 yellow, 1 blue is a golden brown.

To darken it, add blue or black. A shade is a colour mixed with black (tints and shades). Black is strong, so add it a little at a time: 1 part black in 6 takes a mid brown down a long way. More blue darkens as well and moves the brown towards grey.

Warm browns lean red or orange: 3 red, 2 yellow, 2 blue. Cool browns have more blue and look greyer: 3 red, 3 yellow, 4 blue, with 2 white to keep them from going black.

The browns in a paint box often aren't mixed at all. Sienna and umber are earth pigments, dug from the ground. Raw sienna is a yellowish-brown earth whose name comes from the Italian city-state of Siena; heating it turns some of the iron oxide to hematite and gives the reddish burnt sienna (Wikipedia: Sienna). Umber is iron oxide with manganese oxide, which makes it darker than sienna, and burnt umber is raw umber heated the same way (Wikipedia: Umber).

The recipes on this page with those names are colours that look like them, mixed from the primaries, white and black. They match the colour, not the pigment, but they are close enough to stand in when the tube has run out.

The mixer uses a model of paint published by Nathan Gossett and Baoquan Chen in 2004 (Paint Inspired Color Mixing). It treats red, yellow and blue as the corners of a cube, gives each corner a screen colour (no paint is white, all three is a dark brown), and blends between the corners. Their paper says plainly that red, yellow and blue isn't a perceptual colour model but an idealised picture of paint mixing.

Parts are turned into a point in that cube by their ratio, so 2 : 1 : 1 and 4 : 2 : 2 give the same colour. White moves the mix towards the white corner by its share of the paint. Black isn't in the cube, so it darkens the result separately, quickly, the way a little black paint does.

A screen can only approximate paint. Real pigments differ in strength from brand to brand, and a strong blue can swamp a weak yellow, so treat the swatch and the hex code as a guide and test a small amount first. The hex is the screen colour, handy for matching a brown in a design; hex to RGB and hex to CMYK convert it.