Turned up brown uniform on character (6)
I believe the answer is:
nature
'character' is the definition.
(thesaurus)
'turned up brown uniform on' is the wordplay.
'turned up' says the letters should be written backwards.
'brown' becomes 'tan' (tan is a kind of brown).
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'on' becomes 're' ('on' can be mean 'with reference to'**).
'tan' in reverse letter order is 'nat'.
'nat'+'u'+'re'='NATURE'
(Other definitions for nature that I've seen before include "Essence; kind" , "Mother Earth" , "Inherent character" , "Character - our Mother" , "Fundamental qualities" .)