You choose the first pin. 8 options.
You choose the 2nd pin. 7 options (you don't want to repeat the first color).
So for the first two pins, you have 56 combos possible.
You choose the 3rd pin. 6 options.
You choose the 4th pin. 5 options.
So there are `8*7*6*5` = 1680 ways to choose 4 pins (in specific positions) such that no color is repeated.