Historically, khaki was first used to make pants for the British Indian Army that matched their un-dyed leather jackets. In the mid-1800s, the British troops adopted khaki dress as their main uniform.
A darker shade of khaki serge was adopted for home service dress in 1902. The correct shade of "khaki" was also known as "Multani Mitti", meaning "the mud of Multan". Multan was a well known militarycantonment of British India (now in Pakistan).
During the Second Boer War, the British forces became known as Khakis because of their uniforms. After victory in the war the government called an election, which became known as the khaki election, a term used subsequently for elections called to exploit public approval of governments immediately after victories.
Khaki fabric as we know it now.
Today, civilian "khakis" come in all ranges of colors and the term refers more to the particular design or cut of the pants/trousers. In this context, "khakis" have become popular as business casual pants/trousers, and includes other cuts and fabric types (such as chinos).
It is also an increasingly popular style and color for wedding apparel. You will find it blends blends in well with summer weddings (thanks to it's breathability), and beach weddings (thanks to it's easy going, semi-casual look.)