Dirty, like the little boy’s clothes (4)
I believe the answer is:
Here is my best explanation:
'dirty' is the definition.
('blue' can be similar in meaning to 'dirty')
'like the little boy's clothes' is the wordplay.
'like' becomes 'lu' (I can't explain this - if you can you should give a lot more credence to this answer).
'the little' means to remove the last letter (the word is not quite complete).
'boy' becomes 'ben'.
'clothes' indicates putting letters inside.
'ben' with its last letter taken away is 'be'.
'lu' going within 'be' is 'BLUE'.