Zero is considered even. Here is a link that will help explain why.

http://mathforum.org/library/drmath/view/57104.html

Quote
Zero is an even number. An integer n is called *even* if there exists
an integer m such that n = 2m, and *odd* if n+1 is even. From this,
it is clear that 0 = (2)(0) is even. The reason for this definition
is so that we have the property that every integer is either even or
odd.

Mom to DS12 and DD3