Colour of Queen one's turned over (6)
I believe the answer is:
sienna
'colour' is the definition.
(I've seen this before)
'queen one's turned over' is the wordplay.
'queen' becomes 'anne' (I've seen this before).
'one's' becomes 'is' (Roman numeral).
'turned over' is a reversal indicator.
'anne'+'is'='anneis'
'anneis' back-to-front is 'SIENNA'.
'of' acts as a link.
(Other definitions for sienna that I've seen before include "Yellow-brown pigment" , "Pigment obtained from earth" , "Browny-yellow pigment" , "Earthy paint pigment" , "Earth colour containing ferric oxides used as a pigment" .)