Bartman,
When fully mature,
Eumeces fasciatus typically do not retain any of their blue juvenile colouration. People might say they have seen an adult with some blue on their tail, but, because of this blue colouration, these skinks are not yet a fully mature adult.
For example:
This male skink has both juvenile and adult characteristics: a blue tail, some dorsal striping, and an orange throat (typical of a male during breeding season). This male was adult size but because of the coloration I would guess he is a two year old male (and thus not fully adult). Next year he should be a more uniform brown like this one:
Mature female five-lined skinks typically retain the dorsal striping and are a darker bown (closer to black). Mature females also do not have the orange swollen jaws during breeding season.
Aside from the tail, this is a typical female:
I hope this helped!
Cheers,
Ryan