Pick a Pair of Packets
Using 4 of each color
Solution

Going from separate to alternating:

        PPPPBBBB..
        P..PBBBBPP
        PBBP..BBPP
        PBBPBPB..P
        ..BPBPBPBP
      

Back to Pick A Pair of Packets.

To get from the pattern of N P's followed by N B's to the pattern of N pairs of B's and P's takes N steps, but to reach the pattern of N pairs of P's followed by B's takes N+1 steps!

• Ed Barbeau,
  Aftermath: Puzzles and Brainteasers,
  Wall and Emerson, 1995.
• American Mathematical Monthly,
  Volume 67, 1967, pages 974-976.