Check out this fossilized-ink-sac. Researchers confirmed that the pigment in it is chemically similar to the sort used by modern squids, chock full of eumelanin. The head researcher said:
The ‘aha moment’ for me was when we looked at the techniques for chemical bonding and we couldn’t find anything that distinguished the pigment in the fossil from the pigment in a modern-day cuttlefish, which suggests the pigment hasn’t changed in 160 million years. When I think about other evolutionary transitions that just amazes me.