As to changing colour on the outside when cooked (7)
I believe the answer is:
roasted
'cooked' is the definition.
(roasting is a kind of cooking)
'as to changing colour on the outside' is the wordplay.
'changing' indicates an anagram.
'colour' becomes 'red' (red is a kind of colour).
'on the outside' indicates putting letters inside.
'as'+'to'='asto'
'asto' with letters rearranged gives 'oast'.
'oast' put within 'red' is 'ROASTED'.
'when' acts as a link.
(Other definitions for roasted that I've seen before include "How meat might be cooked" , "Severely reprimanded" , "Cooked by dry heat in an oven" , "Cooked (like chestnuts)" , "Carpeted" .)