Fantastic Camilla leaves American in the shade (5)
I believe the answer is:
lilac
'the shade' is the definition.
(lilac is a shade of purple)
'fantastic camilla leaves american' is the wordplay.
'fantastic' indicates an anagram (a fantastic or improbable ordering of the letters).
'leaves' is a deletion indicator.
'american' becomes 'Am' (abbreviation in some contexts).
'camilla' with 'am' taken out is 'cilla'.
'cilla' is an anagram of 'LILAC'.
'in' is the link.
(Other definitions for lilac that I've seen before include "Genus Syringa shrub" , "Fragrant shrub; colour" , "Flowering tree of the olive family" , "Pale purple - flowering tree" , "Pale mauve colour for a flower" .)