You will need:
-A dark item of clothing of your choice
-Bleach
-A empty spray bottle
-Sponges
-Fabric paint or acrylic paint,blue,purple,red,white,yellow. (I used acrylic)
-A toothbrush
-A sharpened pencil
-Newspaper
-Cardboard
1.In the spray bottle make a mixture of half bleach and half water.Lay the clothing item of your choice on the newspaper.So the bleach won't run onto the other side,put cardboard inside the leggings.When you spray the leggings,focus on certain spots where you want your cosmos to be.It should start to turn orange.Let dry for 1 hour.(You can let them air dry or use a blow dryer).Once dry rinse in COLD water and let them dry again.
3.Next water down some purple paint and using another sponge go around the blue in the bleach spots and also anywhere else you desire.
4.Next water down some red paint.Use the red to blend the bleach spots and the blue and purple paint.Then add some white paint in the center of the bleach spots to make them stand out.Also you could add some yellow paint around the white to make it pop more.
Now time to make the stars! Using a toothbrush dipped in white paint , bend the bristles back to make small white specks.To make the larger stars take a sharpened pencil ,making "X" shapes and also dots using the tip of the pencil.If necessary practice on something else before making stars your selected item of clothing.
Now you're done,enjoy !!