It is slate, but only for one bundle in the 600 pr group (the last). The breakdown of a 600 pair is done in 125 pr increments, using the color patterns you all already know. Two wraps are used on these bundles, one two represent the 600 pair group (WRBYV) and one to represent the 5 groups in the 125pr bundle (BOGBS). This hold until pair 501-600 which is only 100pr and hence BOGB and no Slate.