Carbonized bamboo is darker in color because it has undergone a change, not a stain. During the manufacturing of the product, the strips of bamboo are boiled at 200-300 degrees, caramelizing the wood and changing the color (becoming browner in tone). This process also softens the material by approximately 30 %. It gives it a great look and feel, but it's not as strong as non-carbonized bamboos. The surface of the carbonized bamboo has carbon particles promoting an anti- bacterial defense and a smooth touch.
What you need to know before you purchase a Bamboo iPhone 4 case