Colour that's nothing new in fashion (6)
I believe the answer is:
orange
'colour' is the definition.
(orange is a kind of colour)
'nothing new in fashion' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'new' becomes 'n'.
'in' means one lot of letters goes inside another.
'fashion' becomes 'rage' (rage is a kind of fashion**).
'n' inserted inside 'rage' is 'range'.
'o'+'range'='ORANGE'
'that's' is the link.
(Other definitions for orange that I've seen before include "African flower" , "stocking filler" , "Dutch royal house" , "Mandarin?" , "Colour of Northern Ireland unionism" .)