Draw a triangle using a ruler & a chalk
Put a tape on the contour
Put a magazine or a newspaper inside the t-shirt
Pick the white using a sponge
And color the triangle very randomly
Repeat the previous step using different colors (blue, magenta)
***ATTENTION*** To get a better result, remember to mix different shades of the three colors (light blue, bright pink etc...) and blend them!
...Until you get something like this
At this point you're almost done.
-To make the little stars, pick the white using a toothbrush and then rub it with your finger.
-Take away the tape