While most jeans (including most pairs at DC4) are dyed with synthetic indigo, this wasn't always the case. Back in the days natural indigo, harvested from plants like the classic 'Indigofera Tinctoria' or woad ('Isatis Tinctoria'), was the only available option. Natural indigo was widely used countries like Japan, China and India.
When jeans are dyed with natural indigo, they usually don't fade the way you're used to. Don't expect high contrast lines and noticeable results after just a couple months of wear. Natural dye takes years and years to fade, and the result will be a lot more subtle. A proper dye can hold its colour very well.
Natural indigo dye can be harvested from different plants, resulting in different shades of indigo. The amount of dips also has influence on the hue. Also notice that natural indigo is usually more 'green cast' instead of the 'red cast' you've seen on synthetic indigo. Sometimes sulphur is added to the dye to make the result a bit darker. Synthetic indigo has been around since the late 19th century, first released by German company BASF.
Jeans dyed with natural indigo at DC4
We just got a pair of 24oz (and a brutal 27oz after soak!) Samurai S5000AI hand-dyed with 100% natural indigo. 'Ai' is Japanese for indigo (藍), but also for love (愛). The S5000AI is a straight cut with a medium rise, and made in a very limited batch.
These Samurai jeans are also hand-dyed. A very time consuming process, but the indigo is able to penetrate deeper into the fibers. Also, the fibers are less agitated because fewer chemicals are involved in the dyeing process.
The Flat Head and Pure Blue Japan are known for their natural indigo jeans too.