That combination of options is invalid.
$mds-visualization-color-correlation-negativeto represent the range including the edge value (1 and −1 respectively). The subsequent ranges in each should utilize tints of the base color. These tints can be adjusted to match the distribution of the number of ranges, i.e., 25% tints could be used with 8 total legend items, while 30% may be more appropriate with 6 total legend items.
Necessary code documentation can be found in the MBC repository.