In a large bowl mix glue and shaving cream with a spoon.
In a separate bowl or cup, mix 1/2 teaspoon of borax in 1 cup of water. Stir until the borax is dissolved. (To speed up this process, place mixture in a glass cup and microwave for 30-60 seconds.)
Add about a teaspoon of the borax and water mixture into the glue/shaving cream bowl and stir.
Knead with your hands and if it's too sticky, add a tiny bit more borax and water mixture.
Once your fluffy slime recipe is ready. Separate into three pieces.
Add a drop of blue food coloring to the first piece of slime and knead until the entire piece is blue.
Repeat with the other two pieces of slime by adding one drop of pink and one drop of yellow to them.
When all three pieces are colored, add them together.
Gently knead the fluffy slime until you have a pretty mixture of the rainbow.
The longer you knead this slime, the more the colors will become one.