Prince (as he was formerly known) originally acquired uniform in red (7)
I believe the answer is:
ponceau
'red' is the definition.
(shade of red)
'prince as he was formerly known originally acquired uniform' is the wordplay.
'prince' becomes 'p' (abbreviation).
'as he was formerly known' becomes 'once'.
'originally' suggests taking the first letters.
The first letters of 'acquired uniform' is 'au'.
'p'+'once'+'au'='PONCEAU'
'in' is the link.
(Other definitions for ponceau that I've seen before include "Poppy colour" , "Small bridge" .)