Dictionary.com defines khaki as a "dull yellowish-brown." Often a vague term used to describe various light shades of an earth-toned olive to yellowish-brown, khakis are most often associated with the color of some military uniforms.
The basic color of brown is easily made by mixing complementary colors that are opposite from each other on the color wheel. After a shade of brown is made, add in some white to lighten the shade to a more khaki tone.
Orange and Blue
The complementary colors orange and blue make the best brown for a khaki color. Use more orange and slowly add in the blue. Adding more blue darkens the brown. Mix white in the brown to make khaki.
Green and Red
The complementary colors red and green make a darker brown, which can be mixed in with a lot of white to severely lighten the color.
Yellow and Purple
The complementary colors yellow and purple make a muddier brown. A large amount of white must be added to change the color to a light tan.
A small amount of yellow and/or green can be added to a light tan color to create various tones of khaki. A pre-mixed brown paint, such as a raw umber or ochre, can be mixed with white for a quicker khaki mixture.