A group of k elements can be chosen from a group of n elements in \(\frac{n!}{k!(n-k)!}\) ways.
There are 6 colors they can choose from. They want to choose 2 colors.
\((^6 _2)=\frac{6!}{2!(6-2)!}=\frac{6!}{2! \times 4!}=\frac{4! \times 5 \times 6}{2 \times 4!}=\frac{5 \times 6}{2}=5 \times 3=15\)
They can choose two colors in 15 ways.
