Royal color (6)
I believe the answer is:
purple
'royal color' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for purple that I've seen before include "Colour obtained from mixing red with blue" , "Colour associated with imperial authority" , "Colour for aristocracy or emperors" , "Colour between 14dn and blue" , "Red and blue mix" .)