We present a new method for identifying blazar candidates by examining the locus , i.e .
the region occupied by the Fermi  \gamma -ray blazars in the three-dimensional color space defined by the WISE  infrared colors .
This method is a refinement of our previous approach that made use of the two-dimensional projection of the distribution of WISE  \gamma -ray emitting blazars ( the Strip ) in the three WISE  color-color planes ( 18 ) .
In this paper , we define the three-dimensional locus by means of a Principal Component ( PCs ) analysis of the colors distribution of a large sample of blazars composed by all the ROMA-BZCAT sources with counterparts in the WISE  All-Sky Catalog and associated to \gamma -ray source in the second Fermi  LAT catalog ( 2FGL ) ( the WISE  Fermi  Blazars sample , WFB ) .
Our new procedure yields a total completeness of c _ { \mathrm { tot } } \sim 81 % and total efficiency of e _ { \mathrm { tot } } \sim 97 % .
We also obtain local estimates of the efficiency and completeness as functions of the WISE Â colors and galactic coordinates of the candidate blazars .
The catalog of all WISE Â candidate blazars associated to the WFB sample is also presented , complemented by archival multi-frequency information for the alternative associations .
Finally , we apply the new association procedure to all \gamma -ray blazars in the 2FGL and provide a catalog containing all the \gamma -ray candidates blazars selected according to our procedure .