Mounting of princess is brown tinged with yellow (6)
I believe the answer is:
sienna
'brown tinged with yellow' is the definition.
I can't judge whether this definition defines the answer.
'mounting of princess is' is the wordplay.
'mounting' says the letters should be written in reverse (going up in a down clue).
'of princess' becomes 'anne' (I am not sure about this - if you are sure you should believe this answer much more).
'anne'+'is'='anneis'
'anneis' in reverse letter order is 'SIENNA'.
Can you help me to learn more?
(Other definitions for sienna that I've seen before include "Type of earth used as pigment" , "Earthy colour" , "colouring" , "rusty" , "-- Sauce; -- toast" .)