New toot designed for sound of car horn? (3-4)
I believe the answer is:
two-tone
'sound of car horn?' is the definition.
(car horns are typically made up of two notes)
'new toot designed' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'new'+'toot'='newtoot'
'newtoot' with letters rearranged gives 'TWO-TONE'.
'for' is the link.
(Other definitions for two-tone that I've seen before include "With a pair of colours" , "Having mixed colours" .)