Remove colour as it is going inside (6)
I believe the answer is:
whiten
'remove colour' is the definition.
The definition and answer can be both related to change as well as being verbs in their base form.
Maybe you can see an association between them that I don't see?
'as it is going inside' is the wordplay.
'as' becomes 'when' (I've seen this before).
'is going inside' is an insertion indicator.
'when' placed around 'it' is 'WHITEN'.
Can you help me to learn more?
(Other definitions for whiten that I've seen before include "Turn pale" , "Bleach" , "New hit (anag.)" , "Blanch" , "free from guilt" .)