You can expect one to change colour often (4)
I believe the answer is:
dyer
'colour often' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'you can expect one to change' is the wordplay.
I cannot really understand how this works, but
'you' could be 'yer' ('yer' is a dialect form of 'you') and 'yer' is found in the answer.
A single letter 'd' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for dyer that I've seen before include "Cloth worker" , "Person who colours cloth" , "Adder of colour" , "One who stains cloth" , "He changes colour, as it were" .)