It is an error... but not the manufacturer's
The error was by Harrahs in ordering a dollar chip using the same colors and slug design as the existing $2.50. The yellow snapper is scarce, so must not have been on the tables long before being withdrawn and cancelled. There have been some remolded with new yellow plastic to obscure the drill-hole in the slug, but not too many and they can be detected fairly easily. So can the pink ones [g]!