PFN_COLOR_COUNT specifies the number of buckets (colors) into
    which all members of the zeroed page list and all unencumbered
    members of the free page list are sorted. OpenVMS systems might
    derive a preferred page color from a request to map a given
    virtual page and attempt to map that virtual page to a PFN of
    matching "color." This results in less variance in which cache
    blocks are used when accessing that page. This might or might
    not improve performance, depending on the application.

    This special parameter is used by VSI and is subject to change.
    Do not change this parameter unless VSI recommends that you do so.
    If you increase this parameter, you must also increase the ZERO_
    LIST_HI system parameter.