In trouble, a cheetah appears to turn white (6)
I believe the answer is:
bleach
'turn white' is the definition.
(bleaching is a kind of turning white)
'in trouble a cheetah appears' is the wordplay.
'in' indicates a hidden word.
'BLEACH' is hidden within 'trouble a cheetah appears'.
'to' is the link.
(Other definitions for bleach that I've seen before include "Sink and toilet cleaner" , "Peroxide" , "Stuff that whitens, hair or cloth" , "Disinfectant and whitener" , "Make white by sun or chemicals" .)