Dye can end in disappointment (4)
I believe the answer is:
tint
'dye' is the definition.
(tinting is a kind of dyeing)
'can end in disappointment' is the wordplay.
'can' becomes 'tin' (synonyms).
'end in' indicates one should take the final letters.
The final letter of 'disappointment' is 't'.
'tin'+'t'='TINT'
(Other definitions for tint that I've seen before include "(Softer variety of) colour" , "Hue, shade" , "Hair dye" , "Shade; colour slightly" , "A slighth shade of colour" .)