They change colour when doctors take you in (5)
I believe the answer is:
dyers
'they change colour' is the definition.
The definition suggests an adverb but the answer is not.
'doctors take you in' is the wordplay.
'doctors take' becomes 'ds' (I can't explain this - if you can you should give a lot more credence to this answer).
'you' becomes 'yer' ('yer' is a dialect form of 'you').
'in' indicates putting letters inside.
'ds' placed around 'yer' is 'DYERS'.
'when' is the link.
Can you help me to learn more?
(Other definitions for dyers that I've seen before include "14 [SWANUPPING] company" , "Stainers of cloth" , "Colour-changers" .)