Quoted By:
"blue" versions' box legendaries are female (Lunala, Lugia, Zacian etc. and yes, even Xerneas), "red" legendaries are male
Now we only have to find out which version is "blue" and which is "red"
Lilligant, Latios and Illumise are exclusive to White/White2, which points to them being the "girl" versions, but Black/Black2 have Gothitelle and Mandibuzz so idk