If you look at the denominators, they all have a common number they can all multiply into: 24. If you multiply each number in the fraction so that the denominator equals 24, you get this:
1/6 x 4 = 4/24
1/4 x 6 = 6/24
3/8 x 3 = 6/24
Therefore, blue frosting (1/6) is used the least.
Hope this helps: