You probably take the blue in your favorite jeans or denim bean bag chair for granted now, but it was once prized by slave traders, spiritual leaders, royalty and rag traders alike.

A decade ago, Catherine McKinley embarked on a trip through nine West African countries, armed with a fellowship and her fascination for the blue dye. She tells her story in her book Indigo: In Search of the Color that Seduced the World.

The History of Indigo

While indigo traces its roots to India, the African slave trade made it exceedingly valuable on that continent.

"Indigo was more powerful than the gun," McKinley tells Tell Me More host Michel Martin. "It was used literally as a currency. They were trading one length of cloth, in exchange for one human body."

Enslaved Africans carried the knowledge of indigo cultivation to the United States, and in the 1700s, the profits from indigo outpaced those of sugar and cotton.

"At the time of the America revolution, the dollar had no strength, and indigo cakes were used as currency," McKinley says.

The original American flag was also made from indigo textiles.

African Women and the Story of Cloth

Across the ocean, on the African continent, indigo-dyed cloth helped financially empower many African women. Although nowadays, most cloths on the continent are dyed with a much cheaper synthetic color, owning cloth is considered a huge asset. During her stay in Ghana, McKinley learned that cloth is valued more than many women's bank accounts and insurances.

"If you have 300 pieces of good cloth, like a real Madame, well then you have something. A person's spirit is in their cloth," McKinley says.

Each cloth has a name based on its pattern, and it usually tells a cautionary story full of folksy wit: "When my husband goes out, I go out," "Attending school does not mean one would be wise," or "My head is correct."

But for McKinley, tracing the significance of indigo also sets her a on a more personal journey.

"I learnt through looking at the dye pot and how cloth is used and worn, really the value of life and how the color represents life," she says.

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