Gently mist your tee shirt. Like magic, every where that a drop of bleach touches, color is removed. Black turns brown and navy turns pink.
How does this happen? According to http://www.howstuffworks.com/question189.htm,
"When you buy a gallon of bleach at the grocery store, what you are buying is the chemical sodium hypochlorite mixed with water in a 5.25-percent solution. You're buying salt water that has been changed slightly by electricity.
"Natural stains (as well as dyes) produced by everything from mildew to grass come from chemical compounds called chromophores. Chromophores can absorb light at specific wavelengths and therefore cause colors. When chlorine reacts with water, it produces hydrochloric acid and atomic oxygen. The oxygen reacts easily with the chromophores to eliminate the portion of its structure that causes the color."
Anyway, the more bleach you use and the longer you leave on, the more color is removed. So, for subtle effects, mist lightly and go to the next step quickly.
On the example photos, I misted the black tee lightly and in an irregular pattern. For the navy blue tee, I went for a more dramatic tie-dye effect by tying rosettes into the fabric, using rubber bands. I also sprayed more heavily.