After vacation, dress code ignored in ball outfit (6)
I believe the answer is:
livery
'outfit' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for livery that I've seen before include "Distinctive uniform once worn by servants of posh people" , "Uniform worn by male servants" , "Uniform -- suffering from gastric distress" , "The care of horses for pay" , "Feeding and stabling of horses for money" .)