One clad in blue ascending stage (4)
I believe the answer is:
dais
'stage' is the definition.
(I've seen this before)
'one clad in blue ascending' is the wordplay.
'one' becomes 'I' (Roman numeral).
'clad in' is an insertion indicator.
'blue' becomes 'sad' (similar in meaning).
'ascending' is a reversal indicator.
'i' going within 'sad' is 'siad'.
'siad' written backwards gives 'DAIS'.
(Other definitions for dais that I've seen before include "Welshman's" , "Throne platform" , "Platform; podium" , "Raised floor" , "Said (anag.)" .)