This long-sleeved mid drift shirt was navy blue. WAS navy blue, until I tie-bleached it. (Photo color is 100% true to life) It is a blend of cotton, rayon, spandex, and polyester. I twisted it up with rubber bands, randomly, in all different ways and varying the tightness of the knots. The rubber bands were also a wide range of lengths and widths. After soaking it in hot water and bleach, the results were amazing! I had no idea the detail that was going to come out of it. Faces, spiderwebs, insect-like markings...wicked.
I have been trying to achieve an effect with this much detail ever since, and what I have learned is that you won't get it with straight cotton. With fabric blends, yes, and polyester is almost un-bleacheable. Experiment! Take a garment that's permanently stained or ruined, and see what you get. Here are some cotton tees I did: The orange/rust one started off black, and the green was just slightly deeper green: