Everybody in blue back in Texas city (6)
I believe the answer is:
dallas
'texas city' is the definition.
(I've seen this before)
'everybody in blue back' is the wordplay.
'everybody' becomes 'all' (I've seen this before).
'in' is an insertion indicator.
'blue' becomes 'sad' (similar in meaning).
'back' shows that the letters should be reversed in order.
'all' put into 'sad' is 'sallad'.
'sallad' reversed gives 'DALLAS'.
'in' acts as a link.
(Other definitions for dallas that I've seen before include "The Ewing family saga" , "City where President Kennedy was assassinated" , "City in Texas - all sad (anag)" , "City where J. F. Kennedy was assassinated" , "Mysteriously, all sad in the US city" .)