The NPB regulations committee met with 17 bat-makers on Thursday in order to ask them to stick to producing bats that met the leagues requirements. It seems the committee found a number of bats that didn't meat the specs outlined in the NPB rule book.
The committee reminded the bat-makers that bats:
can only come in four colors: natural, dark brown, reddish brown, and black;
and that the wood grain must be visible (visible wood grains apparently makes it easier to spot doctored bats).