Duck's colour that is reflected (5)
I believe the answer is:
eider
'duck's' is the definition.
(eider is a kind of duck)
'colour that is reflected' is the wordplay.
'colour' becomes 'red' (red is a kind of colour).
'that is' becomes 'i.e.' (short for Latin 'id est', 'that is').
'reflected' says the letters should be written in reverse.
'red'+'ie'='redie'
'redie' reversed gives 'EIDER'.
(Other definitions for eider that I've seen before include "Species of duck" , "Down-producing duck" , "Duck known for down" , "Large sea duck" , "Duck supplying down" .)