In snooker what is the colour of the last ball potted?

It can be any ball colour since the game ends when the difference in points is too big to overcome for the other player. That player will then give up. In the majority of games the decision will only be clear at the end and therefore it will often be either the pink or the black ball that will be potted last.

The last part of the snooker game consists of potting the non-red colored balls in order of their value: yellow (2), green (3), brown (4), blue (5), pink (6) and black (7).

The game is formally over (a) when the final pink is potted and the difference in points between the two players is more than 7 points. In this case the black does not need to be potted and if an attempt to pot it is made and the pot was not in, the game ends formally with the black still on the table, or (b) when the final black ball is potted and the two players do not have the same score (if they do, the black ball will be re-spotted)