Looks like you are filtering on a Linked field. In that case, the pick list will show items that are not available in all linked QVWs in gray, and those available in all linked QVW's in regular black. Both types of values can still be selected for the filter normally though.
HTH - Daniel.
P.S - Tutorials on Multi-doc & Linked fields found here: QlikView NPrinting 16 Tutorials - Multi-Document